Here's how that system is supposed to work.
This is the system for a car with an automatic transmission. A black wire with a red stripe comes out of the fuse box, goes out through the firewall, then dives down to the transmission. On the side of the transmission, where the shift linkage is attached, is the neutral safety switch. This switch does two things. It prevents the car from starting when it's not in Park or Neutral, and, it sends power to the reverse lights when the shifter is in the Reverse position. The black wire with the red stripe goes into the neutral safety switch and comes back out of the switch, goes back through the firewall, and the goes to the back of the car with the tail light feed harness, which runs from under the dash, then underneath the driver's side door sill plate, and back into the trunk area.
A manual transmission car has that black wire with the red stripe coming out of the fuse box, and then running underneath the carpet and down through a hole in the floor right behind the shifter, where it goes into a reverse light switch which is positioned in such a way that, when the shifter is in the reverse position, the shifter arm pushes the button on the switch. The black wire with the red stripe then comes back up through the floor, back out from under the carpet, and then joins up with the tail light feed, and goes to the trunk area, just like on an automatic car.
The most common problems with this system are either that the bulbs are burned out, or the ground wire from the reverse light housings have been disconnected or cut, or just got all corroded and funky-looking, or, on an automatic car, the neutral safety switch has gone stupid on you. On a manual tranny car, the same things could happen with the bulbs or the ground, it's just the reverse light switch that goes stupid instead of the neatral safety switch, since it doesn't have a neutral safety switch. If the lights stay on all of the time when the key is in the 'On' position, that is almost certainly a defective switch.
10 comments:
I wanted to add that you can test the reverse switch and reverse lights by disconnecting the pair of 2-wire connectors and shorting the black-red pair together - the pair going through the firewall. The reverse lights should come on.
You can test the neutral switch conveniently too if you have a digital multimeter. Use the low-ohm beep mode of your DVM and connect it to the red-blue pair going to the neutral switch. Shift the car from Park through Low and you should hear beeps in Park and Neutral.
And this leads to a question (finally you say). Testing the neutral switch, I find no contact is made when I'm in the Neutral detent. I have to move slightly past it to get contact. How is the neutral switch adjusted? Does this have something to do with the problem that I have to push extra (actually very) hard to get into Park far enough for the shifter unlock button to pop out. It's not moving far enough for that little bar to pass the high point in the shifter and fall into its slot.
Thanks Veronica!
Bill (again)
Hi Bill.
It sounds like you need to adjust the rod that goes from the drop bracket of the shifter over to the transmission, where the neutral safety switch is attached. From underneath the car, disconnect the rod from the drop bracket of the shifter. Have the shifter comfortably in the park position. Make sure that the transmission is still in park by pulling the rod all the back towards the rear of the car and wiggle it around a bit to make sure that transmission is also comfortably in the park position, and then re-attach the rod to the drop bracket. That should take care of it. And, thank you for taking the time to post the question. Have a wonderful weekend.
I have four black and red wires coming/going from start neutral switch through fire wall. Why do I have four when it sounds like I should have two. Also, how to you "look into" start neutral switch to see what is going on?
Hi Joe.
What appears to be four wires is actually only two wires. The reverse light wire (black/red) comes through the firewall, goes down through the neutral safety switch, comes back out of the switch, goes back behind the dash, and then, basically back to the reverse lights. What you see is two different locations along what is essentially the same wire looping back. Same deal on the red/blue wire. It comes from the ignition switch on the 'start' position, goes down to the neutral safety switch, through the switch, back through the firewall, then out to the starter solenoid.
The switch itself is a permanent assembly that you can't really open up to have a look inside. You can still get a brand new one from any Ford dealership's parts department, though. They are actually pretty reasonably priced.
Hello :) I had a quick question. My lights are both new but or some reason they're weak. Is there any way that I could make them shine brighter? It's not much of an issue, but it's hard to see them(one more than the other) during than the day time. Can you help me out?
Hi, Anthony.
When you say 'new', I'm assuming that this means new housings, lenses and bulbs, but not the wiring from behind the dash back to the trunk area. I think that the first thing that I would do is make sure that the ground wire, which should be attached to one of the studs holding the tailights onto the car inside the trunk, had a good, clean connection. If that seemed to help a little, but still isn't quite 'there' yet, I would unplug and reconnect the neutral safety switch harness at the firewall a couple of times. Sometimes corrosion can build up there, causing a not so great connection. Generally, you should inspect the condition of the wiring and connections and get everything as clean as you can.There is a connection at the accessory feed that is also a common spot for corossion, and that is what supplies power to the system. Other than that stuff, it would be just rewire the whole system, which isn't really a big deal.
I just bought a 65 which was converted from a manual to a c4 automatic with a b&m ratchet shifter. The neutral start switch is gone (obviously).
My question is where should the wires be that will now connect to the two prongs on my shifter for back up lights? I did find the line coming from fuse box that has the three-way connector. The middle wire is still there, but after I follow it awhile it is disconnected under dash. Is this where I need a wire to plug into this and then go up under carpet to the shifter? A wire that goes from a single connector and splits into two?
On a C4, the neutral safety switch is on the side of transmission. There will be what appears to be four wires coming out of the switch, two will be red with a blue stripe and the other two will be black with a red stripe. The black/red are the back-up lights. The wiring comes from the switch and sort of follows the driver's side exhaust up the firewall and goes through the firewall near the master cylinder. With your car having been originally a manual transmission car, the hole in the firewall won't be there. Instead, your car will have a hole in the floor behind the shifter. What you could do is run a wire from the accessory plug, underneath the carpet, down to switch and run another wire from the switch, back underneath the carpet, and into the black/red wire that goes to the tail light harness connector up above the fuse box.
Thanks! I do see two black/ red wires that are coming up from under the shifter. I thought I had tried those two but didn't work. I will try again. What about the wire under the dash that is coming from the three-out plug? (coming from fuse box?)
How this system works is actually pretty simple. Power comes from that plug at the fuse box, travels all the way around the world, goes down to the neutral safety switch along that black/red wire, and, when the transmission is in reverse, continues on through the switch, around the world again, and then joins up with the tail light harness and goes back to the actual back-up lights. The back-up light housings have a wire that grounds out on the tail light housings on one of the nuts holding the tail light housings onto the car. The two wires that you found at the shifter probably go to a manual transmission switch that is attached to the car, or, possibly, have been cut underneath the car and are simply flapping in the breeze down there. You should probably crawl under the car and have a look at what's really there and then proceed accordingly, because people do some awfully strange things to their Mustangs sometimes, and just assuming that everything is as it should be down there and then running power into a blind hole can cause all sorts of weirdness to happen, involving blown fuses, sparks, flames, etc....
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