Mustang Ignition system 1965 and 1966

Here is what your ignition system looks like without that pesky Mustang wrapped around it, along with the wiring diagram. This is a very simple system with a high degree of reliability, even when subjected to the horrible abuse and neglect some people inflict on these cars. How this works is, when the key is in the 'On' position, power goes from the ignition switch to the resistor wire, indicated by the red arrow in the bottom picture. This wire is plugged into a red wire with a green stripe that comes out of the ignition switch. When the power flows through the resistor wire, the voltage is reduced from 12V to about 9V by means of, that's right, resistance. The resistor wire ends at the firewall connector, indicated by the yellow arrow, and turns back into a red wire with a green stripe, which is attached to the post on the ignition coil marked either 'bat' or +, depending on the manufacturer of the coil that is currently in your car. That is the point indicated by the blue arrow. Inside the coil, the power is transformed from 9V to something in the 25,000 to 50,000 volt range, again, depending on the manufacturer of your coil. It sends this blast of power to the distributor by the big wire in the center of the distributor cap that looks like an extra spark wire. The rotor inside the distributor is spinning. The contact point on the tip of the rotor makes contact with the contact points underneath each of the plug locations of the spark plug wires as it spins around and sends that blast of current to the appropriate spark plug wire, which, in turn, causes the spark plug to fire.

In the picture of the distributor top without the distributor cap, the red arrow indicates the condensor, and the yellow arrow indicates the breaker points.

Here is how a breaker point ignition system works. The ignition system has two separate circuits in it. One, called the primary circuit, consists of the primary windings in the coil, the primary lead, which is the wire that runs from the Dist post on the coil to the distributor, the points, and then a path to ground through the casing of the distributor.The secondary circuit is the secondary windings of the coil, the high tension lead ( ninth spark plug wire that goes to the distributor cap), the distributor cap, rotor, and the plug wires. There are two different circuits inside the coil. How this works is power is supplied to the coil through the post marked Bat. When the key is in the 'Start' position power goes out to the starter solenoid through the wire attached to the S post on the solenoid. This closes the switch inside and sends power to the starter, and sends power out through the wire on the 'I' post on the solenoid, which meets up with the wire that goes to the bat post on the coil. Power goes into the coil, runs through the primary windings, out the Dist post on the coil, through the closed points, and then to ground. When the car starts and the key is in the 'On' position, power goes through the resistor wire plugged into the ignition switch connector, and out to the Bat post on the coil and, again, through the primary circuit. When the points open, that breaks the primary circuit, (hence the name 'Breaker Point Ignition' ) and the magnetic field that is built up in the primary coil windings goes through the secondary windings in the coil, and this produces the high voltage needed to actually fire the spark plugs. The high voltage goes out of the coil through the high tension lead, down into the distributor cap, through the rotor and out to the spark plugs, which are grounded through the threaded part of the plug. The points then close, which allows the current to pass through the path to ground through the primary circuit, and the coil builds up another shot of the high voltage for when the points open again. So, if the points are good, you will see a power reading from pretty much any metal part of the distributor when the points are closed, because the distributor is the ground for the primary circuit. If there is no power reading from the metal of the distributor, that means that power could not pass through the two contacts of the points, and that can't happen if the points are in a usable condition. Power makes it to one contact, but doesn't make it to the other = points are no good.If you have a power reading on the metal parts of the distributor when the points are open, that means that the primary lead is shorting itself out on the case of the distributor somehow, probably where it goes through that hole in the side of the distributor. The fix is to replace the primary lead and try not to scrape it up when it gets shoved through the hole in the side of the distributor. If the primary circuit checks out ok, but the plugs still aren't getting any spark, that is generally either a torched out distributor cap or rotor, bad plug wires or spark plugs that are fouled or just plain worn out. It's actually a pretty simple system once one understands how these components all work together to shoot sparks down to the plugs.

It is important that this system be properly maintained by means of a regular tune-up, which consists of replacing the spark plugs, distributor cap, rotor, points and condensor, along with inspecting the wiring periodically to make sure that nothing is damaged or worn out, or has a bunch crud or corrosion building up on a connection. These cars will keep on chugging down the road in an astonishingly poor condition, but it is costing you in a lot of ways to do that, namely, poor fuel economy and poor performance. Since all of the parts involved in this tune-up are really, really cheap, and readily available from any auto parts store, and the level of expertise needed to perform this tune-up is amazingly low, it makes no sense not to.

There is a problem that people encounter, which seems to be quite baffling to them, but results in 'car won't start'. If, when you turn the key to the start position, the car cranks fine, sounds like it started, but dies instantly when the key returns to the On position, that is almost always one of two things. Either the resistor wire is dead, and needs to be replaced, or, the car has a factory tach, and the tach has died. You could get a factory tach on these cars if A) you had a 65 or 66 Shelby GT-350, you purchased one of the over-the-counter Cobra or Rotunda tachs from your local Ford dealer, or your car had an original rally pac. How the factory tachs were wired was, two of the wires that came out of the back of the tach were connected in-line with the resistor wire at the ignition switch. You unplugged the resistor wire from the red wire with the green stripe near the ignition switch and plugged the two tach wires into the two ends of the ignition wiring. When the tach dies, it takes the car's ignition system with it. The fix is to unplug the tach wires and plug the resistor wire back into the red wire with the green stripe that comes from the ignition switch.

Starting system

Here is the system responsible for starting your car for you. At a glance, you will immediately see that this is a veeeeery simple system. How this works is, when you turn the ignition key to the start position, that sends power to the ' S' post on the starter solenoid. It helps to think of the starter solenoid as a switch. When power goes to that 'S' post, that activates the switch and completes the circuit running from the positive post on the battery to the starter. When the key is released and it returns to the 'on', that turns off the switch and the starter quits turning because it has no power going to it. Cars equipped with an automatic transmission have a thing called the neutral safety switch. The wire going from the ignition switch to the 'S' post on the starter solenoid makes a trip through the neutral safety switch. This works as a kill switch so that the car can't be started while it's in gear. The transmission shift lever must be in either Park or Neutral. Manual transmission equipped cars don't have a neutral safety switch.

A starting system problem that is frequently mis-diagnosed is what is sometimes referred to as ' the starter hanging up'. That's when the starter just keeps right on cranking after the key has been returned to the run position. People run out and buy themselves a new starter, or beat on the starter with a hammer or something, when, if you think about it, the starter itself is the one thing that you know for sure is NOT the problem. It's down there cranking like crazy, working beautifully. The reason that it's doing that is because it is still getting power when it's not supposed to, so something along the line of power flow must be the problem. And that is the starter solenoid. It is continuing to supply power after it was supposed to stop doing that. The most common cause of the starter solenoid hanging up is a weak battery. Insufficient current combined with having system engaged far longer than it should be makes stuff start heating up. When the solenoid gets too hot, the contacts of the switch inside it try to weld themselves together.

Another thing that can cause what appears to be a starter problem is a bad ignition switch. You have returned the key to the run position, but, internally, the switch has refused to comply with your wishes and is still over there in the start position. But, it is far more common to have it be the starter solenoid.

Mustang Alternator and charging system 1965 and 1966

This is a system which seems to be a prolific source of confusion and despair for people, but it is actually quite simple, once you understand it. For all practical purposes, the only thing that your battery is supposed to do is supply power to start your car. After the car starts, all of the lights and gauges, and the motor itself, is powered by the alternator. The alternator also makes sure that the battery is fully charged for the next time you want to start your car. The alternator generates power and sends that out into the cars electrical system. This system, like all other electrical systems, can't just push power out into the void. The power also has to have a way to get back to where it started from, or, a ground. That's why they call them electrical circuits. The power has to take the entire tour. You have a black wire with a yellow stripe coming off of the alternator post marked ' Bat' that goes to the hot side of the starter solenoid. This is the same post that your positive battery cable goes to from the battery. You have a black wire with a red stripe that is attached to the post on the back of the alternator marked 'Grd'. This is, that's right, the ground. This is basically one wire with three ends. One end is attached to the alternator, one end is attached to the engine block on the same bolt that the negative battery cable is attached to, and the third end goes through the headlight harness and is attached to the radiator core support with one of the screws that holds the voltage regulator onto the car. You have a white wire that is attached to the back of the alternator on the post marked 'Fld. This wire goes over to the voltage regulator and is going into the terminal marked F on the side of the voltage regulator. It should be the terminal on the bottom with the voltage regulator mounted on the car with the plug thingy on the driver's side. There will be a yellow wire that goes from the voltage regulator terminal marked 'A' over to the hot side of the starter solenoid and that's all that there is for the actual functioning of the alternator itself. The alternator generates nearly 15V, it goes to the voltage regulator and gets knocked down to 12V, comes back and goes into the electrical system of the car. This part of the system is the same, whether you have an alternator light or an ammeter gauge. The differences between the two systems are all in the way that the charge indicator tells you what's happening with the system.

The charge indicator light works like this. There is a white wire with a black stripe attached to the post on the back of the alternator marked 'Sta'. That wire goes to the voltage regulator and then winds it's way to the charge indicator light and miraculously turns green with a red stripe along the way. There is another wire that is black with a green stripe that jumps off of the red wire with a green stripe that comes from the ignition switch and then goes to the charge indicator light. The light will have two wires coming out of the back of it, one black with a green stripe from the ignition switch and one green with a red stripe coming from the voltage regulator. The two pictures of the back of an alternator show how the wires are supposed to be attached to the back of it. The one with three wires attached to it, without one attached to the stator post is for a car with an ammeter gauge, and, the one with four wires attached to it is four a car with the charge indicator light.

The ammeter gauge works in one of two ways. On a 66 model car, it will have a red wire that goes out to the hot side of the starter solenoid, and a yellow wire that splices into the black wire with a yellow stripe that also goes to the hot side of the starter solenoid.
On a 65 model car that came with either the GT package ( performance/image option) or the pony interior ( Interior Decor Group) the ammeter gauge doesn't actually have any wires attached to it. It has that big black wire with the yellow stripe passing through a metal loop which is attached to the back of the ammeter gauge without actually touching anything. If I didn't have any understanding at all about automotive electrical systems and was asked to pick which one of these two systems normally doesn't work, the 65 system is the one that I would pick, since there aren't any wires attached to the gauge. But, I would be wrong. The 65 ammeter gauges almost always still work forty plus years later, and the 66 ammeter gauges, more often than not, didn't work brand new. There is nothing strange about your 66 ammeter gauge not working. It's nothing personal. They treat everyone like that.

Mustang gauges 1965 and 1966

This is the wiring diagram for the gauges on a 66 or a 65 that has either the GT (Performance/ Image Option) package or the Interior Decor Group, a.k.a. Pony Interior. If you click on the diagram, you will be able to see all of it, instead of just the left side. What I'm dealing with here will just be the water temp, fuel and oil pressure gauges. The ammeter gauge is a free-standing, independent system that has absolutely nothing to do with the other three gauges. The gauges on your car make up a system that supplies you with some very useful information when it is working correctly, and is a very simple system to understand and repair. What you have is a black wire with a green stripe on it coming from the back of the ignition switch going to the instrument cluster voltage regulator. The ICVR takes the 12V from the switch and, by means of thermally actuated contact points, knocks the voltage down to about 6 volts. The reason that Ford did it like this was because they had all of these perfectly good gauges of a proven level of reliability that were originally intended for a car with a 6V electrical system, and, rather than redesign and manufacture all new stuff, they just used a voltage regulator in the system. Ok, now that we have gotten that out of the way, you still have that black wire with the green stripe going from the ignition switch to the ICVR. On the other end of the ICVR you have a wire, still black/green that splits off to the three gauges. That wire plugs onto the what is the driver's side of the gauges when they are mounted in the dash. This wire brings power to the gauges. On the fuel gauge there will be a yellow wire with a white stripe that goes to the fuel sending unit in the gas tank. On the water temp gauge there will be a red wire with a white stripe that goes to the water temp sending unit, located towards the front of the intake manifold on a V8 and towards the rear of the cylinder head on a 6cyl. There will be a white wire with a red stripe going to the oil pressure sending unit, down near the oil filter. The wires going to the sending units work as a ground, with the sending unit itself determining how 'good' of a ground the gauge is getting.

If all three gauges are acting stupid on you, the problem is either the ICVR or the wire bringing the power to it. There is a dash to chassis ground wire that is hooked to the mounting screw of the ICVR, but that is what makes your dash lights and stuff go goofy on you. It doesn't have anything to do with the gauges.

If one or two of the gauges seem to be functioning normally and only one or two of them is having trouble, then the problem is almost always either the sending unit, the wire going to the sending unit, or the wire going from the ICVR to the gauge. Once in a blue moon it will actually be the gauge itself, but that happens so seldom that it really isn't even worth mentioning.

If the gas gauge is the one acting goofy the first thing that you want to do is to unplug the wire from the sending unit and, with the key in the 'On' position, ground that wire out to a suitable place on the car that isn't insulated from the rest of the car. The leaf spring shackles, for example, are in a handy location, but are completely insulated by the bushings. If the gauge pegs to full, the problem is inside the tank. The problem inside the tank is, far more often than not, the float isn't floating anymore. The brass floats cost like 5 bucks, whereas, a Ford sending unit costs nearly two hundred, and the repops cost about fifty and normally don't work. If the gauge does not peg to full, then the problem is either the wire going to the sending unit or the wire coming from the ICVR to the gauge.

If the water temp gauge is the one acting funny, again, ground the wire out somewhere and see if the gauge pegs. If yes, replace the sending unit. They also are cheap. If no, it's probably the wire going to the sending unit. People have the annoying tendency to cut that wire and then strip back both ends and tie the two ends back together. Don't do that. A brand new engine gauge feed only costs about twenty bucks, and you'll have brand new stuff that will work reliably for many years to come. If money's a bit tight, use some proper connectors of the male/female plug-in variety and wrap that to insulate it. All of what I just said about the water temp gauge is also true about the oil pressure gauge.

This isn't complicated. You can do this, and you can do it right.

Setting the points in your distributor

Contrary to popular opinion, setting the points in your distributor is not a dark art. It is actually a very simple procedure. In the picture on the bottom, the point gap, circled in red, is closed and there is a yellow arrow pointing at one of the 8 ( or 6 on 6 cyl car) distributor cam lobes. In the picture on the top, the points are open and the point gap is indicated by the yellow arrow. After removing the distributor cap and rotor, and then installing the new points, rotate the crank shaft in a clockwise direction from facing the motor with a 15/16 socket wrench on the big bolt in the middle of the crank shaft pulley until one of the bumps on the distributor cam is holding the points all the way open. If the points don't seem to open at all when you rotate the crank, loosen the screws and move the points in closer to the middle of the distributor, so that, as the distributor turns, the points open and close.. With the two mounting screws loose enough to slide the points back and forth, move the points to the place where the gap is correct. On a 6 cyl car the point gap should be .024-.026 inches, on a 260 or a non-hipo 289 the point gap should be .014-.016 inches and on a hipo 289, or K code, the point gap should be .019-.021 inches. Then tighten up the two mounting screws. A hipo 289, the K code, is supposed to have a dual point distributor. On these, you do what you just did twice, as there are two sets of points in there instead of just one. The reason that the hipos got this type of distributor was because the motor was designed to run at much, much higher RPMs than the other motors, and in extremely high RPM situations, something called 'point float' can occur. That's when the points don't really close quite right and sort of hang around the outside area of their travel and flutter. Having two sets of points greatly reduces the frequency and severity of this happening.

Breaker point ignition systems have fallen into ill-favor in most circles, but personally, I don't think that they deserve this. A whole bunch of cars kept chugging down the road for a whole bunch of years running on breaker points. I have a pertronix unit in the distributor of my car, because they function consistantly until the day that they fail entirely, kind of like a light bulb, but I also keep a set of points and condensor in the glove box of my car, because that is something that I know for sure will work, and is a very simple swap, in case I have to do that on the side of the road.

Just a quick update. I now have the points back in the distributor instead of the pertronix. I got tired of having something in my car that I didn't understand and, consequently, didn't trust.

Date codes

Ford used a few different formats of date coding the parts on a 65/66 Mustang. On sheet metal parts, such as fenders, hoods, shock towers, etc... there will be a number that goes like 4 12 2D. The first number is the month, with this one being, as you might suspect, April. The next number is the day of the month. The next one is the shift that stamped this particular part, in this case the second shift, and the letter indicates the plant that produced this particular part. The D is Dearborn, MI. C would be Cleveland, OH. W is Windsor, Ontario. There is nothing to indicate the year on the sheet metal parts. The picture is from the floor of my car underneath the back seat and this part was stamped on May 21st on the 3rd shift in Cleveland.

On cast iron parts, like cylinder heads, engine blocks, etc.. the format is different. They go like 4M13. The first number is the last digit of the year, the letter is the month and the next one or two digits are the day of the month. The picture of the engine block shows a date code of 5L20, which is november 20th of 65. The picture of the cylinder head shows a date code of 9A9, which is January 9th of 69. On the letter designations a lot of people 'miscount' because they didn't realize that Ford did not use the letter I (eye) because it looks too much like the number 1.

The aluminium parts, like bell housings, some water pumps, etc.. Had a system that is a little bit weird looking if you are unfamiliar with how it works, but is actually pretty simple. There will be a two digit number, indicating the year, inside a circle that has some bumps around the perimeter. On a really, really nice one, it looks like a pie sliced into 12 pieces, but most parts haven't withstood the march of time nearly well enough to be able to see that. On this picture of the starter hump on a five-bolt bell housing, you will see the number 64, indicating, as you might suspect, 1964, and 4 little bumps. That means April, so this bell housing was cast in April of 1964.

Nothing to it.

The date codes used for the scheduled production dates of cars was simply a two digit number, indicating day and a letter indicating month. There is sometimes a little bit of confusion surrounding the letter designations for the 65 model production year. The sheduled production date of the first Mustangs were in march of 64, so the letters A and B weren't used then. They started with C for march of 64, going C-H for march through august of 64, skipping the letter I and using the letter J for september and going J-M september through december, jumped back to the letter A for january of 65, B for february of 65 and picked back up with Q for march of 65, and went Q-V for march-august of 65.

The carburetor tag will have a date code stamped on it which will have 3 digits, one number followed by two letters. The number is the year, followed by the month and then the week of that month. The one in the picture says 6CC, which would be 1966, march, the third week of the month. Sometimes you will see the letter 'E' as the last digit on the tag, which is the fifth week of the month. If the first falls on a friday, production for that month would have fallen across five different weeks.

The distributor date code is in the same format as the cast iron parts, except for it is stamped into the housing, instead of cast in, like on an engine block or cylinder head or something.

1965 Mustang wiring diagrams