Here is a diagram of how the brake lights work on your car. If you click on the diagram, you will then be able to see the entire diagram, instead of just the left half that you see now. I made the diagram as big as possible so that it would be easier to see. Now,moving back to how the brake lights work, there are actually two different circuits. The bulb in the tail light socket is a dual filament bulb. Power comes from the headlight switch over to the brake light switch, which breaks the circuit. When you step on the brakes, that completes the circuit in the switch, and power then proceeds from there to the turn signal switch, which sends the power on back to the tail light sockets, lighting up the brighter of the two filaments in each of the tail light bulbs. When the tail lights are not on, and you have your foot on the brake pedal, both of the brighter filaments should be on, until you activate the turn signals. Then one bulb stays light and other blinks full on/all the way off. When the tail lights are on, like when driving at night, that activates the dimmer of the two filaments in each bulb. When you step on the brake pedal, again, both bulbs are full on. When you signal a turn, one bulb will be full on and the other will blink full on/ half on, because one filament is still getting power as a tail light from the headlight switch.
The most common problems with the brake lights make up a pretty short list. At the top of that list is the bulbs are burned out in the tail lights. Always check that first. Then, it would be the plug-in connector to the tail light housing, or the socket on the housing itself, has gotten all corroded and funky looking. After that would be the brake light switch ( part # C5AB-13480-C) has gone bad. Replacing this isn't a big deal at all. It's hanging on the brake pedal arm, up above the steering column. You just unplug the two-wire connector, remove that pin that goes through the peg that the switch and the master cylinder push rod are hanging onto, pop the master cylinder push rod off of the peg and the switch will fall out into your hand. Nothing to it. On an earlier car ( like mine) the brake light switch is screwed into the front of the master cylinder, but the wiring system is the same. The only difference is the actual location of the brake light switch. Sometimes, the turn signal switch is the culprit, but normally a bad turn signal switch will make your car go retarded on you in some other way. Occassionaly it will be a problem with the wiring or the head light switch, which is the source of power for the brake lights.
How to trouble shoot the brake lights should go like this. First, check the bulbs and the sockets in the tail lights. Next, unplug the connector from the brake light switch and take a paper clip, bend it in such a way that you can stick that into both slots of the wire connector. Try not to have your skin touching any bare metal on the car when you do this, as it might deliver a little bit of a shock to you. It isn't dangerous, but it also isn't very enjoyable. If the brake lights come on, replace the brake light switch. If the brake lights don't come on, check with a volt meter to see if power is reaching the connector. If no, find out why not by checking the headight switch and connector. The wire that supplies power to the brake lights is coming out of the same slot in headlight switch connector that has the big yellow wire that supplies power to the horns. If yes to power reaching the brake light switch connector, check with the volt meter to see if power is leaving the turn signal switch at the two wire connector coming out of the steering column from the turn signal switch. If yes, your problem is in the wiring along the tail light harness somewhere. If no, your problem is in the turn signal switch, or the wiring going to or from it. Problems with this system, just like any other, are diagnosed by starting at one end and systematically going through the circuit until you find the break. You can do this.
You've mentioned in other "how tos" to check the ground leads. True for the brake wiring too - I had one intermittent tail light ground.
ReplyDeleteI've decided to replace the tail light harness because they're kinda beat up. More importantly the fuel sending cable is very fragile, especially from the heat from the tail pipe. I find it peculiar that they run it so close to a hot surface. In your experience do you rerun the harness from the trunk to the front, or, from the front to the truck? For the headlight harness, I tied the new to the old and pulled the new through the lower radiator mount. Can I do this to pull the new tail light harness with the old one?
Many thanks again!
Bill
When running a new tail light harness, you you can't really pull it through with old harness. If everything is as it was when it left the factory, there are some little clips at various points along the way holding the tail light harness in place, and there are a whole bunch of pretty sharp edges along the way that slash some bald spots in the new wiring if they didn't cut clean through. The best way to run the new harness is to go ahead and remove the driver's side kick panel, scuff plate and rear trim panel. You'll have to snatch the back seat out for that. I always run them from front to back, but, it really doesn't matter which direction you go in.It really isn't a big deal to go ahead and get everything out of the way, take a minute and route everything in such a way that it won't be rubbing on one of those sharp edges as you go down the road, or have a trim screw poking it or something, especially in light of the headaches that a rushed installation can cause on down the line. Hope that helps.
ReplyDeleteThank you! I should have said the kick panel, scuff plate and rear panel are removed. I was still worried about getting from the opening below the rear window and into the trunk (convertible btw). So I pulled the old wires into the trunk until the end was near the rear window opening. I taped the new end in the trunk and use the old just to get over the wheel and into the cavity below the rear window. Untaped it and pulled the old back out. This worked ok.
ReplyDeleteOne thing - there were no clips from the trunk to the first clip under the scuff plate. Does the wire just lay loose in the rear cavity?
One thing curious - why does the fuel sender wire run across the bottom of the trunk to the opposite side? Seems the cable is open for being damaged by luggage across the whole width of the trunk. Why didn't it just drop out of a hole on the left side?
Again, thanks for your time and expertise,
Bill
There are also supposed to be a couple of clips sort of underneath the rear window. It's kind of late here right now, but, in the morning I'll go snacth the back seat and quarter trim panel out of my car ( also a convertible)and take a couple of pictures to show you what they're supposed to look like and where they go.There are more than a couple of sharp corners and edges in that area.
ReplyDeleteAs far as the routing of the gas tank sending unit wire goes, it does seem like they could have dropped it down on the driver's side and used a shorter wire. The wire is actually pretty save in there in the original configuration of the trunk area, though. There was a couple of clips attached with the gas tank mounting screws along the back edge, and the car would have had a trunk mat sitting on top of all that, so, the wire was safe enough. One would really have to try pretty hard to damage it. Hope that helps.
Perhaps someone could help me troubleshoot my 65's dilemma? Driver's side brake light out, passenger rear side turn signal out. Both bulbs fine. Could it be a problem in the same wire?
ReplyDeleteMy first guess on that one would be that the turn signal switch is bad. The minimum number of wires that could be causing the problems that you describe would be two, both of which come from the turn signal switch. If the brake light works on the passenger side, but the turn signal does not, that would just about have to be a turn signal switch problem, because it's the same wire that does both of those things. If it can do either one of them, it can't be the wire itself.
ReplyDeleteHi Veronica and thank you for your help. I have a 1966 mustang and I had a brake light problem. I used your procedure for checking out the problem and it was great. I went step by step as you said how to trouble shoot the problem and when I got to the part that said to check the connection at the light switch bingo, the wire had pulled out. I seated it again and that solved the problem. I would have never thought of that. Now I have a problem with the turn indicators. The right one would not blink so I bought a new switch, installed it and it fixed the problem for about a week. Now when I put on the left or the right both blinkers blink like the emergency switch is on. I disconnected the wires to the emergency switch but no change, they both still blink. Can you help me figure out whats gone wrong? thanks in advance
ReplyDeleteHi Veronica,
ReplyDeleteI was hoping you could help me. I have a rear indicator problem with my 66 convertible.
First of all left side is no problem, works as it should, front indicators and dash indicator lights are no problem, they work as they should.
My problem is the rear right. they do not light at all. No brake light, no indicator light and no emergency flasher going there. It does work with the headlights on.
I have checked voltage there and 0V goes to that side. I have checked the two pin connector coming from the steering column wiring and when the left is on and flashing, 12V goes to the green wire (left side) and 0V to the orange(right side) but when i put the right indicator on i get 0V to the green (which I expect) but still 0V to the orange (right side).
Would this mean my turn signal switch is the problem?
I have checked globes, I have checked and swapped over pigtails.
Can you suggest any other troubleshooting before I buy and install a new switch?
Regards
Peter (Australia/Melbourne)
Hi Peter.
ReplyDeleteIf, when you hit the right turn signal, no power is showing on the orange/blue wire that's leaving the turn signal switch, there are really only two things that could be the problem. Either that wire has figured out a way to break itself inside the steering column (highly unlikely) or, it's the turn signal switch itself. Replacing the turn signal switch isn't really a big deal, though. You just disconnect the negative battery cable, because the horn circuit is hot all of the time, remove the steering wheel, unplug the two connectors at the base of the steering column, cut those connectors off of the old switch, leaving enough wire hanging off of the connectors to be able to get a grip on them and identify which wire is which, remove the three screws on the retainer holding the actual switch mechanism onto the steering column assembly, remove the two small screws that hold the tapered collar onto the hub that the switch is attached to, and snatch the old switch out, wrap a little tape around the ends of the wires on the new switch so that you can feed them back through the route that old wires came out of, remove one old wire from a connector, install the appropriate new wire, and do that eight times.It's a good idea to do the wires one at a time like that if you haven't done this a whole bunch of times before because it is very, very easy to hook the wires up wrong, and possibly fry your new switch, or have the horns start honking in time with the signal flasher when you hit the left turn signal or something. Then, just put every thing back together and you are ready to go.
Great cite; I appreciate the wisdom. My issue is that the brake lights on my 66 mustang work, but I have to be almost stomping the pedal to get them to work. Is there a way to get them to come on sooner? It has a booster for power brakes (if that matters). Any ideas would be greatly appreciated.
ReplyDeleteThanks.
It sounds like your brake light switch has seen better days. Replacing it is easy and pretty cheap.
ReplyDeleteVeronica, your info on fuse box and wiring was invaluable. my husband had been working on wiring for weeks and took it to a "pro" with no luck. Tail lights were coming on when Ignition was on and dimming when courtesy/interior dimmer was dimmed. I read your previous blogs and found it very interesting. The previous owner had converted to new blade type fuse box but had connected wires incorrectly and did not match wires to original wiring. It took us two days, but when we finally went by your "old type" fuse box and wiring, we finally got it! Everything works as should be. Thanks so much! My husband was very glad I read your instructions out to him over and over again. Don't stop sharing!
ReplyDeleteThank you SO much for sharing your knowledge! April and I thank you with honor, and our respect.
ReplyDeleteMe----> S. Bruno
April----> APRIL
http://scottbruno.com/images/Must-Hanger1-2.JPG
I have no brake lights, but if I turn the tail light pigtail just right, sometimes I will get a passenger brake light, but no driver brake light...rear blinkers work, and all other lights work, running lights, headlights, dash, courtesy, etc.
ReplyDeleteI used a light probe on the two wire switch coming from the steering collumn, and I only get power when the blinkers are switched on, no power at all when brakes are pushed. I have a new brake switch (has power), and new headlight switch. I made sure the tail-light housings are grounded (had to scrape off the new paint to enure it is metal on metal.
If I have no power at the two wire connected under collumn, please tell me that isn't a bad turn signal switch?
Your expertise would be GREATLY appreciated.
Thanks!
Kari
Hi, Kari.
ReplyDeleteThe first thing that I would do is unplug the brake light switch connector and see if I had power on one of the wires. If, no, then the wire that brings power from the headlight switch is not doing its job. This could be the wire, or the connector at the headlight switch or the brake light switch, or possibly the wire itself. If power is making it to the brake light switch, I would check the wire that goes from the brake light switch to the turn signal switch at the turn signal switch connector to see if it shows power when the brake pedal is pressed. Let me know wht you find out.
Hi Veronica,
ReplyDeleteI found your blog while trying to diagnose my light issue, unfortunately my problem is reverse of what everyone is talking about here. my tail lights stay on constantly. Directionals work, brake lights work but i cant get my tail lights to go out. When i park the car i have to unplug the brake light switch so i don't drain the battery. note I recently had the speedometer out to paint the dash and i believe the headlight switch shorted in the dash. I just recently replaced that in hopes that was the problem. An other note is that the speedometer lights no longer light up.
Any ideas?
It sounds like the knob shaft isn't seated all the way. If it doesn't go all the way in, that will make the tail lights and the front parking lights stay on. I would try removing the shaft, wire wheel it to clean it up a bit and re-install it, making sure that it goes all the way in. That should take care of it.
ReplyDeleteHello Veronica,
ReplyDeleteMy 66 Mustang Brake lights stay on constantly... I have replaced the switch and they are still on.. I tried to adjust the push rod for master cylinder and they're still on. I'm lost please help.
Also, head light dimmer switch turns dash lights off when turned to the Left?? Is that normal?
Thanks, John
Hi, John. The dash lights thing that you mentioned is normal. It's supposed to do that. On the brake lights, is this something that all of a sudden happened after you've had the car for a while, or has it done that since you've had the car?
ReplyDeleteHowdy Veronica,
ReplyDeleteLet me start by saying that you are the (wo)Man. I very much appreciate your blog -- sure beats a greasy old shop manual.
I'm having problems with my right (passenger side) break light. It don't work. It comes on when I turn the lights on, but the brighter filament does not work when pressing the break pedal. The bulb is new. I replaced the headlight switch. Blinkers are not working either so I'm leaning towards the problem being the turn signal switch. However, I wanted to check with you first.
Thanks!
Hello. Thank you, that is very kind of you. A lot would depend on what exactly you mean by turn signals not working. If the appropriate lights come on, but don't flash, that is going to be the turn signal flasher. If nothing happens at all, that would probably be that the power isn't making it to the flasher. When a turn signal switch goes bad, it almost never has every aspect of it fail at the same time, because that switch has an awful lot of different connections. On the brake light thing, I would start by unplugging the two wire connector coming out of the turn signal switch, push the brake pedal and see if both wires show power on a volt meter. If yes, the problem is further down toward the tail lights.If that is the case, I would unplug the right tail light connector and plug it into the left tail light and see if it works on the other tail light. If yes, the socket on the tail light housing is bad. If not, the problem is in the wiring of the tail light harness or the connector itself. I would run some easy tests to see exactly where the break in the power flow was. Let me know what you find out.
ReplyDeleteHello,
ReplyDeleteThanks for the response.
I got the car in 1985 and everything worked fine. I had to leave it covered in a tarp outside for 4 years from 1998-2002. It has been garaged since, but the damage was done and I'm in the process of getting it back on the road (new engine, gas tank, etc, etc etc...)
None of the instrument cluster lights work because there is corrosion between the bulb and the ground of the housing (I get power going through the wire). So I need to clean the housings of that gunk so a good contact can be made. Annoying but no biggy.
I don't have any blinkers in that the front blinkers do not come on at all. Regarding the brake lights, today I verified that I'm not getting power to the right brake light at the connector from the steering column ( I unhooked the two pin connector next to the 6 pin connector below the steering column). I'm getting power to the left brake light but not right brake light.
So I have traced backwards from the bulb and the next thing up the line is the turn signal switch. Does the brake light switch attached to the brake pedal split off to left and right brake wires before getting to the turn signal switch? If so I can check that. Or does the left and right brake signals originate at the turn signal switch? Since I don't have any lights coming on when turning on the blinkers, I'm thinking that the turn signal switch is screwed up.
Also, my horn and headlights don't work but one step at a time...
Thanks again for your help!
Michael
That would be the turn signal switch, then. There is only one wire going to the turn signal switch for the brake lights, but two coming out. However, with what you have said about the history of the car, it could easily be case that you have corrosion in the six wire connector which is causing the horn problems. With that being said, I would still get a new turn signal switch, along with a new headlight switch, ignition switch, starter solenoid and wiper switch. Sitting idly for years is generally not kind to components like that.. If you don't have problems with the other switches now, you certainly will in the near future. The ignition switch, starter solenoid and headlight switch can be purchased at any major auto parts chain store, and are very reasonably priced.
ReplyDeletehowdy Vernoica,
ReplyDeleteAll switches are now new exes for wiper switch.
Put in new turn signal switch today. Both brake lights now work. The problem with the headlights not working was because of dirty contacts at the dimmer switch. Once I cleaned those up I have headlights, both low and hi beam.
Despite putting in the new turn signal switch, I am still not getting blinkers (I.e the lights do not come on, nor do they blink). Also, my horn does not work.
Any quick thoughts about those?
thanks,
Michael
I think that on the turn signals not working I would start at the flasher and make sure that power was reaching it. The power starts out at the ignition switch, goes to the flasher, and then to the turn signal switch. If power is making it to the flasher, I would then check at where power goes into the turn signal switch for the turn signals at the six wire connector. It's sort of a 'start at one end and go through in steps with a volt meter until you find the break in the power flow. On the horns I would run a jumper wire from the positive battery cable to the place where the wire plugs into the horn and see if that made the horn work. If yes, I would do the same 'check in steps' thing, starting at the steering wheel. Let me know what you discover.
ReplyDeleteHello Veronica, I'm having a brake light and turn signal issue with my 66 coupe. The driver side rear brake light and turn signal work. The passenger side brake and turn signal do not work. If I turn on the running lights... both back running lights are on. I checked the bulbs and they're good. I also cleaned the bulb sockets of corrosion. Also the grounds on the rear tail lights. Do you have any suggestions please? Thanks!
ReplyDeleteI think that I would, just for fun, swap the bulbs from the left and right tail lights, just to make sure that it wasn't a problem with the bulb. If that's ok, I would twist the passenger side connector around on the passenger side with the turn signal on and see if was trying to start working. If is trying to start working, I would try cleaning that connector up. If that doesn't do it, replace the connector. If the turn signal does not try to start working,I would plug the connector from the passenger side onto the the driver's side tail light housing and see if the problem moved over to the driver's side. If yes, I would check that orange/green wire for power with a volt meter. Let me know what you find out.
ReplyDeleteHi Veronica, I pulled the brake connector wires off at the brake pedal and jumped across it with a wire. The driver side lights up and the passenger doesn't. I cleaned both brake light fixture connectors up. When I pulled off the connector at the rear brake/turn signals and checked continuity, I have 12.3 Volt on the drivers side and zero on the left. I cleaned the grounds too, same results. I also pulled out the passenger fixture and hooked it up to the drivers side... it worked. So, eliminated the fixture and bulb being bad. I guess no power to that wire means a break in the wire? Or, could it be the turn signal switch at the steering wheel? I thought from your blogs I read that if you pull the connector at the brake pedal, jump across it, and you get power to the back lights, It's not the turn signal switch...? I'm stumped... Any more suggestions please?? Thank you!
ReplyDeleteIf you have no power on the passenger side wire, then that is certainly a problem. If you look at the wiring coming out of the steering column, you will see one 6 wire connector and one 2 wire connector. The 2 wire connector is what what runs the rear turn signals and brake lights. If you unplug that 2 wire connector and press the brake pedal, both of those wires should show power on the side coming out of the steering column. If they both show power, you have a break in the wire somewhere between that connector and rear tail light housing. If one of them shows power but the other does not, the problem is in the turn signal switch. What I meant with that thing about bypassing the brake light switch thing was, if you bypass the brake light switch and both brake lights come on, the problem is not with the turn signal switch. If only one of them comes on, the problem could easily be in the turn signal switch. There is only one wire involved in the brake lights before the turn signal switch, so, if there is a problem with either the brake light switch or the brake light wiring before the turn signal switch, neither one of the brake lights will work because they are powered by the same wire. If one works and the other doesn't, that eliminates everything between the turn signal switch and the battery as candidates for the problem, because that is all the same wire. Again, let me know what you find.
ReplyDeleteHi Veronica, I pulled the 2 wires off of the column like you said and they BOTH have power. So, It's a problem with the wire running from the tail light to the connector. I will do my best to start tracing it to that connector from that tail light. My next question would be... is there a good way of doing this? I see it runs into the inner truck wall and where does it go from there? Again, thank you so much for your time and expert wisdom! Also, the fact that your doing this for free for all of us newcomers is magnificent!
ReplyDeleteThis is probably going to sound like a lot more work than it actually is. If you remove the scuff plate in the bottom of the door jamb, the driver's side kick panel, the back seat bottom and back seat back, then the driver's side rear window crank and driver's side lower trim panel, you will have easy access to the entire tail light harness. The only things on that list that can be a little tricky are the way that the set screw holding the window crank on might be stripped and the rear seat bottom can sometimes be a pain in the rear to get out. On the seat bottom, all that you have to do is push the thing towards the rear of the car and then lift up on front of it, and that will pop it loose. Sometimes they will fight you on that, but, there aren't any screws or clips or anything that you can't see. Normally they pop right out like they're supposed to, but, occasionally they don't. You'll also need some sort of ratcheting screwdriver for a couple of the screws on the scuff plate. As I said, this might sound like a lot of work, but, really, this entire process will probably only take you maybe 15 minutes. A real ambitious fellow with a bit of foresight would also take advantage of this opportunity to lubricate the quarter window tracks. Let me know how it goes.
ReplyDeleteAnd, thank you. That is very kind of you to say that stuff. I assure you that it is my pleasure. I see absolutely no reason at all for people to have to cough up big bucks going to the 'gurus' to have something done that they can easily accomplish themselves if they had a little bit of simple information on how their car does the stuff that it does. So, here I am. (insert smiley face)
Veronica, I have a 66. When I pull the headlight switch one click, the parking lights and tail light come on momentarily ant hen they go off. Then they randomly flash like they are trying to come on. When I pull the switch out the rest of the way to turn the headlights on, the headlights are on but they pulsate but never go out. While this is happening i can hear the switch pulsating. I changed the switch but still have the same problem. It does this whether the car is running or not. Does that rule out the voltage regulator? If it is a ground issue, where do I start?
ReplyDeleteThe headlight switch has an internal circuit breaker. What you are hearing is the breaker tripping and resetting itself, which is also what is making the lights do the weird things that they are doing.Since changing the headlight switch did not help anything, what you probably have is a short in the wire that feeds the tail lights.
ReplyDeleteHi Veronica great info I'm having an issue with my rear turn signals it only occurs when the light switch is off when i turn either left or right turn signal on both tail lights flash but the front signals and dash lights light up accordingly. If i turn the parking lights or the running lights everything works as it should. Ive replaced the turn signal switch and ive cleaned up all contacts and grounds at the tail lamps as well as all the lights please help thank you so much for the invaluable information
ReplyDeleteThat's odd. Is this car a 66, a 65 that came with gauges from the factory, or a 65 that came with idiot lights?
ReplyDeleteIts a 65 with gauges I'm unsure exactly if they are factory or added later as this car was originally a 6 cylinder and the po swapped it for a 289 and repainted the car
DeleteIts a 65 with gauges but not rally pac I've tested wires all the way up to the dash I'm debating running different wires but i dont have the money for a new harness I'm really just trying to get it back on thr road at this point lol
ReplyDeleteIts a 65 that came with gauges
ReplyDeleteIts a 65 that came with gauges
ReplyDeleteCool. For your car to have come from the factory with gauges, it ould have to have come with either the GT package, which it did not, or, with pony interior, which it could have. If you pull the instrument cluster out a little so that you can see the bottom edge of the hole that the instrument cluster fits into, the bottom edge of that opening will be either straight, or, it will have a downward dip in the middle to accommodate the round speedo in the five-dial instrument cluster. I'm trying to figure out a way that I could make a car do what yours is doing if I wanted it to do that, and, knowing how your car came originally is going to help with that.
ReplyDeleteWhen i get home this evening I'll go out and check i would be surprised if the car came like that but it could have ive always wanted to do the research and see exactly how the car came
ReplyDeleteWhen i get home from work I'll go check it out. Ive always wanted to research the the vin and see exactly how the car came even though there probably isnt very much still the way it came from the factory. I was wondering if i could run a new tail light wire
ReplyDeleteI found out when i got back around the car that my good ol dad whom ive been helping keep this old girl running forgot to mention that he had changed the tail light bulbs to led bulbs which is a great improvement over the old style however requires a different flasher which he was unaware of so I'm sorry for the inconvenience. I just ordered the flasher tonight so it'll be a week or so before i can see if that solves the issue so i am going to swap bulbs and see if that cures it and I'll let you know. Now i feel like an idiot for sure
ReplyDeleteThat certainly sounds like something that would cause the problem that you have. Turning on the taillights could pull enough power to make the turn signals work like they're supposed to. And, it is no inconvenience to me at all. Trying to help people is what I do, and, everytime something like this comes up, I get to see the questions that I forgot to ask, and that helps make a little better at this. I was thinking that, if this is a 65 that came with idiot lights, it would just about have to be a ground problem of some sort. It never occurred to me that you might have LEDs in the taillights. Don't beat yourself up too bad. Half a century is a long time for a car to be on the road, and the ones that are still running have had all sorts of things done to them over the years. :)
ReplyDeleteYou are certainly a valuable asset to all the people like my dad and I who are trying to keep these beautiful stangs on the road thank you so much for all the great information you provide and i will let you know how things play out thank you again this is always my first stop for ideas.
ReplyDeleteHello Veronica, thanks again for all your help. Here's my brake/tail light problem. Its a 66 coupe. The harness was cut up to install a trailer light harness but I've pulled that all out and re-spliced the wires how I think they're supposed to be. Turn signals work fine but no brake or tail lights (back up lights stay on as well). I don't have power to the tail lights...black and orange wire i think? I've read several posts that say check the ground but I don't see a ground wire for the tail lights, I see it for the back up lights...where is the ground wire supposed to be for the tail lights? Oh, license plate light doesn't appear to get power either
ReplyDeleteIf the rear turn signals work then your problem with the brake lights is not in the trunk area. Coming out of the turn signal switch you have a six wire connector and a two wire connector. That two wire connector is for the both the rear turn signals and the brake lights. One wire is left turn and left brake light and the other is right turn and right brake light. With the rear turn signals working, just knowing that tells you that the brake light problem is somewhere between the turn signal switch and the headlight switch. I would start by bypassing the brake light switch and see if they come on light that. If yes, then you need a new brake light switch. If no, there is a break in the wiring somewhere between the headlight switch and the turn signal switch.
ReplyDeleteThe reason that you can't find the ground wire for the tail lights is because there isn't one. They ground out on the body of the car through the taillight housing. The license plate light is in-line with the tail lights, so, if the tail lights aren't getting power, then neither will the license plate light. The tail light wire is black with no stripe. The only black wire back there that has a stripe is the reverse light wiring, which is black with a red stripe.
Dear varoooom Veronica,after reading all your post I'm about sure I know what the problem is but I want to make sure . The drivers side brake light dose not come on . I remove the 2 pin connector an have power to both sides when the turn signal is blinking but when I step on brake only passenger side gets power no power on the drivers side Is that the turn signal switch ? thanks in advance! An the fact that you are a girl is awesome!
ReplyDeleteYup, that would just about have to be the turn signal switch. And, thank you. That is very kind of you. Although, since I'll turn 42 in a couple of weeks, I don't think 'girl' is the most accurate description possible. At least I've been around long enough to see some real change happen on that. 20-25 years ago the consensus was that there was something wrong with me. (insert smiley face)
ReplyDeleteLol, coming from a 51 year old that makes you smokin hot! Because you like old cars you know how to work on old cars and you probably know a Zeppelin song or two! Ha ha. Enough joking I can't begin to tell you how helpful your browser is! After reading it I kinda knew what it might be, but only because of what you have already posted! You are so kind to help everyone with your knowledge! It's a rare find an much appreciated!
ReplyDeleteHello, I have a 64 1/2 that is having some brake issues. When I press the brake, no lights come on. If I turn the signls on, both work. When I press brake and turn right signal on, brake light come on and signal works. When I press brake and left signal, only signal comes on and no brake light. I have replaced the brake light switch, bulbs, and bulb housing, and it has not fixed this problem. Any help would be appreciated. Thanks! Cody P.
ReplyDeleteSorry this took so long, it's been a little hectic here. That would just about have to be a faulty turn signal switch. If anything about the brake lights work under any conditions, it can't be the brake light switch or the wire going from the switch to the turn signal switch. The same with the wiring after the turn signal switch. The variable seems to be the turn signal switch itself.
ReplyDeleteMy 65 Mustang's brake lights won't work. Tail lights, turn signal work. Wiring is worn, brittle. Right bulb won't stay tightened. Should replace wiring, get new tail light kit (buckets), change to pigtails connection and also get new brake light switch?
ReplyDeleteI would start with checking the brake light switch. From the turn signal switch to the tail light housings, the rear turn signals use the same wires as the brake lights, so, if the rear turn signals work, the problem is not with the wiring between the turn signal switch and the tail lights.If you disconnect the connector from the brake light switch on the brake pedal, unfold a paperclip, and stick that in both of the slots in the connector, the brake lights should come on. If they do, in fact, come on like that, you need a new brake light switch. Let me know what you find out.
ReplyDeleteI have a 64.5 Mustang. Brake lights and turn signals all work. However when I step on the brake, with either the left or the right turn signal blinking, the respective blinker stops flashing and stays on steady (front and rear). The green light on the instrument panel goes to steady as well. When I let off the brake, the turn signal (and green instrument light) begins flashing normally again. I also have a delay when turning on the blinkers, until the turn signals begin flashing. Not sure if it's related. Any suggestions on where to start looking would be greatly appreciated.
ReplyDeleteDisregard my previous post. After hours of studying the exterior lighting wiring diagrams, making a matrix of what lights work...when (the problem became worse when I turned on the running lights), buying a $100 turn signal switch and spending hours checking wires...I found the problem. I replaced the tail/brake light buckets last summer. After trying everything I could think of to narrow down the problem, I was about ready to start replacing the turn signal switch. As a last resort though, I decided to swap the old tail/brake light buckets back in, before replacing the turn signal switch. To my complete surprise, everything worked with the old buckets in. I eventually noticed on the new buckets that the little brass contacts in the bulb socket were touching, on both light buckets! Using a pair of needle nose pliers, I separated the contacts so they weren't touching. I put the new buckets back in and voila! Everything worked. I now have an unused Scott Drake turn signal switch...if I end up needing one some day.
ReplyDeleteVeronica,
ReplyDeleteI have 1966 mustang whose brake lights only work when I have the headlights turned on? Is this normal? I suspect not, because would be a hassle to make sure to turn on/off the headlights during day driving (when headlights not generally needed. With headlighhts on both my brake lights and turn signal switches work.
Any ideas? Thanks in advance.
No, that definitely is not supposed to be the case. I've been trying to figure out how I would make my car do that if I wanted it to, and the easiest way that I could come up with was to take the wire that supplies power to the brake light switch, which does come from the headlight switch, and connect the headlight switch end to something that is only hot when the headlights are on. It could be that someone has gotten creative behind the dash of your car, possibly as some sort of 'repair'. Maybe there was a problem with the headlight switch connector, maybe the headlight switch itself, and somebody just bypassed the problem area and drove with the headlights on all of the time.
ReplyDeleteVeronica, your page is such a huge help.
ReplyDeleteLet me tell you briefly what my problem is. Hopefully you can help. I've owned many early Mustangs, and they always seem to cause me grief in the taillight area. My latest, a 65 Mustang 2+2, is acting up some. Basically, the taillights stay on no matter what, and when I depress the brake, nothing happens. I also just installed new parts on the rear drum brakes. The lights were not malfunctioning like this before I installed the brakes. What could be the problem? I'd really rather not replace the brake light switch. haha. Thanks. Jim
Thank you, Jim, that is very kind of you. Having worked on the rear brakes did not do anything to the tail lights. As you no doubt noticed, (insert smiley face) there are no wires attached to anything in there. Having the tail lights stay on all of the time is almost always some sort of headlight switch problem, usually due to the knob shaft not being fully seated. The first thing that I would try is pecking on the knob lightly with a hammer, as if it where a big nail, and see if that makes them go off, or , possibly, flicker. If it does, I would remove the knob shaft and wire wheel the dickens out of the shaft, and then reinstall it. As far as the brake lights go, if the brake light switch needs to be replaced, it needs to be replaced. The brake lights do care how difficult it is to reach the switch. Granted, it is not a lot of fun to snake your hand up in there, but, it is what it is.
ReplyDeleteThanks. I'll give the headlight switch a try. Let's hope it's that. I've replaced two brake light switches, and it ain't fun. =) Appreciate the reply. You're always a life saver. Jim
ReplyDeleteHi Veronica, great advice! I have a '66 Coupe, I've recently changed the brake switch, but now anytime the battery is hooked up, the brake lights are on and the turn signals are blinking. If you depress the brake pedal they will stop blinking and go solid. Any advice would be great. Thanks!
ReplyDeleteThat's odd. The turn signals and the brake lights use the same filament in the tail light bulbs. Are saying that, when you connect the battery, it looks like the emergency flashers are on and the tail lights are off, and then you step on the brake pedal and the brake lights work like they are supposed to? Or, does it look like both the tail lights and the emergency flashers are on, and then you step on the brake pedal and they work like they are supposed to? Also, when they are flashing, do the fron turn signals also flash?
ReplyDeleteThanks for the quick response, it seems that anytime the battery is connected, the emergency flashers and the brake lights are on, when you step in the brake the emergency lights stop flashing and are just on... and yes the turn signals flash and then go solid on as well when you depress the brake pedal.
ReplyDeleteThat is a strange problem. The only thing that I can think of that all of that stuff has in common is the turn signal switch. Replacing the turn signal switch should take care of that, but, There isn't really any way to be certain without first replacing the turn signal switch.
ReplyDeleteHi Veronica, I have been reading all of your posts and have a question about grounding the tail light housings in a 1965 Mustang. I recently had the car painted, at which time the tail light panel was replaced and the entire inside of the trunk was sprayed with truck bed liner. My issue is, with the light switch off the brakes work, with the light switch on nothing and also when I step on the brakes the dash instrument lights flash. The right rear blinker works, the left blinker causes both rear lights to blink. I think I am going to scrape some of the bed liner off of the inside of the tail panel to get metal on metal. However, I wanted to run it by you to see what your thoughts are and how best to tell if I am getting a true ground to the tail light housings? The only thing I haven't replaced is the turn signal switch and the tail light housings. Thanks in advance.
ReplyDeleteAssuming that everything worked normally before the paint job, a bad ground could cause strange things like this to happen. I would start by taking a wire with an alligator clip on each end and attach one end to one of those studs sticking out of the back of the taillight housing and attach the other end to something that I knew had a good ground. The most obvious thing with a known good ground would be the negative battery post. If the license plate light seems to work, the rear bumper should work as a ground location.
ReplyDeleteHi Veronica, I wanted to follow up that my problem has been resolved. Turns out that the taillight housing connection was either going out previously or developed a short in it. I ordered and installed two new taillight housings and everything is now functioning as it should be. Thanks for the help and I will stay tuned in to your Blog, invaluable information.
ReplyDeleteThanks
Hi Veronica. I have an interesting issue for ya. I have a 1964 1/2 Mustang and I'm having a strange brake light issue. Everything works as it should except that my brake lights don't light unless I press heavily on the brake pedal. The master cyl is full of fluid, blinkers work, tail lights work and brake lights kick in when pedal is pressed heavily. The switch obviously works. When I pull into my garage and come to a complete stop I can see my brake lights are working because I see the reflection however, when I'm driving around town I have people tell me the lights are not working. I tested this out by applying just enough pedal to stop the car and verified I can stop the car without the brake lights illuminating....it's really only when I'm at a complete stop that I can put enough pressure on the brake pedal to get the lights to illuminate. What could be causing this? Is there an adjustment in the brake pedal? Thanks for any help you can offer.
ReplyDeleteMy first guess would be that your brake light switch is in the process of failing on you. Your car should have the switch that screws into the front of the master cylinder, so, it could also be that some tiny chunk of crud from inside the master cylinder is partially obstructing the opening, but, if I was going to remove that switch to check it, I would go ahead and stick a new one in there.
ReplyDeleteHello Veronica. I have brake lights and turn signals, but no tail lights ( lights at night). I have led lights in the back. I also have changed the brake switch in the master cylinder. I'm sure the issue could be a simple fix but don't know how to verify what is causing the problem. Could it be the turn signal switch? Thanks for any help.
ReplyDeleteHello Veronica. I have brake lights and turn signals but no tail lights for night. My lights are led and I changed the brake switch in the master cylinder. I think it is the turn signal switch that is the problem but not sure. How can I test to make sure what the problem is? Thanks for any help.
ReplyDeleteGood evening,
ReplyDeleteFirst off, I want to compliment you on such an incredibly helpful site. I have a 1966 Mustang that I just finished a few electrical updates. I replaced the instrument cluster bulbs, (filters had deteriorated compromising illumination and bulbs were also failing) and replaced the backup light fixtures due to wires separating from the housing and the chrome pitting. I tried to replace the headlight switch but the replacement would not seat the control rod, so I am waiting on another one. I either have a coincidental anomaly or I somehow did something wrong. Because now, my driver's side brake light and left turn signal does not work. But right side brake light and turn signal works fine. Both tail lights illuminate when I turn on the headlights. And the real kicker is - when I apply the brakes, my instrument cluster lights illuminate! (Just the instrument cluster, not turn signals nor high beam indicator). If it was just the failure of the driver's turn signal and brake light, I would presume somewhere within the light switch- brake switch/turn signal circuit, but the instrument cluster illuminating when the brake pedal is depressed, without the light switch at either first or second pull level is rather bizarre. Could this be a grounding issue, and if so, where?
I genuinely appreciate your or anyone else's insight on this.
Hi Michael,
ReplyDeleteI had the same issue when the brake pedal laws engaged the instrument lights would illuminate. The issue was the tail light housing being grounded to the body. I had recently had my car painted and while doing so the tail light panel was replaced and painted. I ended up roughing up the area where the tail light housings make contact with the panel and everything resumed working as normal. Uncertain if you have replaced the housings recently but that is where you should start.
Hi,guys. Whenever there is a problem with one of the rear brake lights/ turn signals, the problem is going to be somewhere between the turn signal switch and the problem rear light. My first guess would be that there is some kind of a problem with the tail light housing. Possibly a bad ground, like Terry suggested, possibly the rear of the actual bulb socket I would try taking the passenger side wire and plugging it onto the driver's side tail light and see if it still did weird things. If no, plug everything back like it's supposed to be and check again. It could be that corrosion or some kind of crud was making the brake light short out on the tail light circuit, which would make the instrument lights come on.
ReplyDeleteVery helpful information folks, and I will proceed as suggested, but a followup question - how does the ground differ from the tail light function vs the ground from the brake light/turn signal function? Exactly how does each ground work? What completes the ground between these two? The deeper I can get in the weeds and comprehend all this the better chance I can work through the symptoms en route to a successful outcome.
ReplyDeleteBTW - when I pulled the tail light boot connector off the back of the tail light put a test light in the tail light boot center connector and engaged the left turn signal, nothing happened - (I should have included this earlier)..
I genuinely appreciate your expertise, and look forward to pursuing your suggestions as soon as I can find time during tolerable windows of our current mid-atlantic heat wave...
I will be sure to report back so we add yet another anecdotal problem/solution scenario to this fantastic blog.
Thanks again!
Very helpful information folks, and I will proceed as suggested, but a followup question - how does the ground differ from the tail light function vs the ground from the brake light/turn signal function? Exactly how does each ground work? What completes the ground between these two? The deeper I can get in the weeds and comprehend all this the better chance I can work through the symptoms en route to a successful outcome.
ReplyDeleteI genuinely appreciate your expertise, and look forward to pursuing your suggestions as soon as I can find time during tolerable windows of our current mid-atlantic heat wave...
I will be sure to report back so we add yet another anecdotal problem/solution scenario to this fantastic blog.
Thanks again!
The brake lights and tail lights use the same ground. If you look at the tail light bulb, you will notice that it has two filaments, and, that there are two contacts on the base of the bulb. Power comes into the bulb through those contacts on the base, goes through the appropriate filament, and leaves through the metallic casing of the bulb. That is the part that is in contact with the socket in the tail light housing, which makes contact with body of the car. Assuming that everything else on the car is as it should be, the power goes through the body of the car to the ground strap which goes from the firewall to the engine, and the negative battery cable is attached to the side of the engine block,at the same place as the alternator ground, completing the circuit. The electrical current for any component in your car makes a lap starting from either the positive battery post or the 'BAT' post on the alternator goes through the headlight harness to the area behind the dash inside the car, out to the appropriate components, then grounds to the body of the car, then back the firewall, then through the engine and back to either the negative battery post or the ground post of the alternator.
ReplyDeleteUnderstood. With this in mind, when I put a test light on the left boot connector to the housing, (and ground the test light to the trunk latch), the test light illuminates when I turn on the headlights but not when I engage the left turn signal nor press the brakes. When I do the same to the right tail light boot connector, the test light illuminates for all three functions appropriately. So it seems that it might be a turn signal switch issue.
ReplyDeleteIt is possible that the turn signal switch is indeed the culprit, but, it could also be the green/ orange wire going from the switch, or, possibly, the boot connector itself. If you look at the driver's side of the steering column you will see 8 wires coming out. There is a 6 wire connector and a two wire connector. I would unplug the two wire connector and run the same test on the two wires coming out of the switch that you did on the tail light sockets. If you have power on them both when you press the brake pedal, the problem is not the switch. If one of the wires is dead, that would be the fault of the turn signal switch.
ReplyDeleteI was finally able to replace the turn signal switch and yes, indeed, that was the culprit. Your review of the symptoms and narrowing it down to the turn signal switch was spot on. Thanks so much for your expertise - this is such an extraordinarily helpful blog.. Now of course I have yet another anomaly. My dash instruments lights keep going out. I might have an issue with the turn signal cylinder "tubes" interrupting ground. I had to fabricate a custom replacement by cutting and overlapping toilet paper roll tubes and they might be compromising a clean metal connection of one or both of the turn signal lamp sockets to the instrument panel. I hope to re-fabricate them this weekend, giving more clearance for the socket-to-dash connection, but I was also hoping to get a better idea of the wiring signal flow for the instrument lights to determine other possible issues, since I am able to get the lights back each time I replace the fuse, but then it seems to blow when I hit a decent bump in the road..
ReplyDeleteI genuinely appreciate any insight you or other readers can provide..
THANKS!