start-run-charge-power distribution circuits

This is going to be long so get your favorite snacks and drinks and enjoy.

I hope that these pictures and explanations will help when it comes to the amp meter and start/run circuits for the 1969/1970 cougar XR7. This could apply to the rest of the XR7 cougars as well but I don’t have schematics for those years of cars but the function is the same.

Knowing ford, they were good at carrying over to other years. Even my 1988 thunderbird turbo coupe shares a lot of the same wire colors and circuit numbers.

I will focus on the under hood wires first because most of the time that is where they get burnt from the exhaust manifold or from a bad short. Or maybe you have a car that has had the wires hacked. This is often misunderstood as to how it is wired or even how it works.

This part of the ammeter/ignition/start/charging circuit is different than the standard cougar – completely – different.
The diagrams that are from ford, I find a little cluttered/scattered. I drew up a simplified version with the paint program that deals with just this part of the circuit.

If you plan on splicing in a set of wires from another cougar, due to burnt wires you will need one from an XR7 if you have an XR7. Better yet would be to replace the whole harness.

It is a tuff job for most but not too hard, just a time consuming project. That way there is no question about its reliability later on. This would depend on the amount of damage that you have and if the damage goes on past the firewall.

I found errors in the original XR7 diagram in the alternator/power distribution circuits. It has missing wires from the alternator output lead to the battery.
Without it the battery would never get charged. Also missing is the power feed to the ignition switch. Well it looks like it is missing anyway unless you study the whole schematic/book.

Those two wires start at the splice where the [yellow-(654)] for the amp meter is located. From that splice there is a big [black/yellow-(37)].
That wire runs through the firewall to a splice under the dash that has the rest of the wires for power distribution.
The other missing wire is the one that runs to a two-conductor alternator plug. Described later in this post.

Those two missing wires should confound anyone that is trying to fix an issue with the alternator/power distribution circuits, unless you have (all) of the schematics for the car and you can read them and understand how ford wrote them. There may be updated versions of the schematics but I have not seen them.

The first picture is of my 1970 XR7 wires unwrapped to the firewall, that show how the amp meter is wired. The wire that is between the two rubber knots (splices) is the shunt wire for the ammeter.
Most people do not know what it even looks like so this post should solve that riddle. The shunt wire is not present on the standard cougar as well as many other differences.


If you have schematics at hand and want to follow along here is a brief description of the wire colors and circuit numbers.

IE: [black/green-(297)] = the wire is black with a green stripe and the circuit number is 297.
Some times a circuit will branch or has a connector or even a device installed in the path and will be labeled [black/green-(297A)] or B-or C and so on.
It is still the same wire/circuit path but just means that there was a device/branch/connector in its path.

Also the fuse links and the resistor wires can be identified by the insulation used to cover those wires. Both wires feel like it has a rubber coating on them and is not smooth to the touch as the rest of the plastic coated wires.

At the top of the first picture I will start at the solenoid battery post.
The fuse link is labeled. This is a short wire spliced onto the main power feed wire. It is [Black-(38B)].

Through this link power is both taken from the battery and power is put back into the battery. I believe that the cougars have a black fuse link from the factory, mine does.

If your car runs then there is nothing wrong with the fuse link. If it blows you will have a completely dead vehicle. You might have a hood light that works. But that’s it. Oh and if you have a convert, the top will work. They have their own fuse/circuits attached to the battery post of the solenoid.

You can test the link easy by giving it a bit of a tug. If it stretches a lot when pulled it is shot. Just be sure not to yank too hard. You could pull it apart.

Attached to the fuse link at that first splice you will see a red wire
[Red-(655)] spliced with it.
That red wire feeds one side of the ammeter. It goes directly to pin-5 of the instrument cluster connector.

Next there is a 24-inch big black wire [black-(38)] that leads to the next splice.
That is the shunt wire for the ammeter and at the second splice it has a yellow wire [yellow-(654)] spliced into it. That yellow wire feeds the other side of the ammeter gauge. It goes directly to pin-6 of the instrument cluster connector.

Note here: the ammeter is a circuit all by itself. If the red wire and the yellow wires were removed the only thing that would cease to function is the ammeter. (The bloody thing doesn’t work anyway so who would know.) :crazy:

The ammeter works by measuring the voltage drop across the shunt wire due to the small resistance that is in between the red and the yellow wires.
If current is being drawn from the battery the meter should move to the D discharge side of the gauge.
If the current is being put back into the battery the meter should move to the C charge side of the gauge.

The longer the shunt wire is in length, the greater the voltage drops across it. Making the gauge deflect farther IE: it will deflect farther at a lower amp draw. turning your 60-amp gauge into a 40-amp gauge for example.

The only time that I have seen the ammeter gauge move more than ½ needle width is when there was one heck of a short/smoke/fire……………. Other than that it will move very little.

I will say again the ammeter circuit is all by its self so if you think it is causing a no power problem then look some where else for the problem.


Lets start where I left you. At the splice, that is at the end of the shunt where the (yellow) wire is [yellow-(654)] .
From that splice is a big [Black/yellow-(37)] that runs up to the firewall and another black wire [black-(38)] that leads off from that splice to a two-conductor plug that plugs into the alternator harness.
These two wires look like they are missing in the schematics. More on the alt wiring later.

The second picture/drawing is of the under hood wiring. The big [black/yellow-(37)] wire is the main feed wire for the whole car.
It will start from the second splice at the shunt where the [yellow-(654)] wire is located.
Then that [black/yellow-(37) wire runs up to and past the firewall to a splice just above and to the right of the steering column, above the windshield wiper switch that will branch off to other circuits. Ignition switch/headlight switch and also the fuse box.

If you look at the third picture that I drew up. I have that splice labeled with the branches. One wire (BIG YELLOW) [yellow-(21)] that comes from that splice runs to the female plug that the ignition switch plugs in to.

There is another wire, big [black/orange-(25)]. That wire goes to the head lamp switch.

From that same splice a big [black/yellow-(37A)] wire runs down to the fuse box. That powers stuff that does not need to have the ignition switch turned on IE: cigarette lighter/interior lights.


Ok, let’s look at how this works.
Back to the drawings you will see the big [yellow-(21)] that comes from the splice with the big [black/orange-(25)] and big [black/yellow-(37A) wires.
The big [yellow-(21)] wire goes to the ignition switch and is hot at all times and it’s only fuse is the fuse link at the solenoid.

When the key is turned to the run position it will apply power through the ignition switch to a Big [black/green-(297)] wire on the opposite side of the ignition switch connector that is next to the big [yellow-(21)] wire.

That wire will run to a splice and changes to [black/green-(297A)] that runs down to the fuse box.
Also in that splice is the [violet-(30)] resistor wire that runs over to pin 12 of the instrument cluster connector and supplies power to the instrument voltage regulator that is mounted on the back of the cluster panel.

The big [black/green-(297A)] wire has power to it in the run/accessory position of the ignition switch.
That wire will power all circuits that operate when the key is in the run/accessory position. IE: radio/wipers/turn signals/instrument voltage regulator.


In the start position, power is sent through a [red/blue-(32)] wire from the ignition switch (top left of the ignition switch connector) to the neutral safety switch connector and changes to [red/blue-(32A)] after going through the switch before it is applied to the (S) post of the solenoid to activate the starter.

Inside of the solenoid is a built in switch that sends power to the (I) POST of the solenoid when it is activated. That will apply power to a [brown-(262)] wire from the (I) POST back to a three conductor connector at the firewall behind the engine for the ignition coil while the starter is running and sucking up all the juice.

The brown wire at the three conductor connector is also spliced inside that connector to the [pink-(16A)] resistor wire for the coil.

It will make sure that the coil will have enough power to start the car. The purpose of this is to bypass the [pink-(16A)] current limiting resistor wire and supply extra battery power to the coil. Once the switch is returned to the run position the [pink-(16A)] resistor wire supplies the power to the coil.

Also, when the ignition switch is in the start position, there are two posts on the ignition switch (lower left bottom of the connector in the fourth picture) that are separate from the power source. Look at the fourth picture it is of the female connector for the ignition switch from the main harness.

Note that one post is to the ground circuit [black-(57A)] that wire runs over to the instrument cluster connector pin 18. And the other wire that is located on the post just above it that is from the ignition switch, runs off to the dual brake warning lights switch that is mounted on top of the brake distribution block and is a [violet-(977A)] .

That wire [violet-(977A)] runs from the ignition switch down to the big square firewall connector.
It then changes to [violet-(977)] on the other side of the firewall and connects to the dual brake switch.

Then from the other side of the dual brake switch that wire runs back through the square firewall connector. Then that wire [violet-(977) runs back up to the instrument cluster connector pin 16.
This is a warning lamp prove out switch that lights up the warning light in the dash in the start position. The lights will go out when the switch is returned to the run position.


As mentioned above the big [black/green-(297A)] wire to the fuse box is hot in the run position.
There are two other wires that need to be hot in run as well and they are on a different part of the ignition switch. Look at the switch diagrams. Top right post of the connector. There is a [green/red-(904)] wire and a [red/green-(16)] wire at that post.

Due to the 40 years that has gone by. That wire has changed color at the connectors. I had to peel back a lot of tape before I could verify that it was actually red/green. Red+green=brown when mixed together.

The [red/green-(16)] or red/brown wire, which ever you have, runs up to the tachometer connector.
The tachometer is part of the coil/ignition circuit, without the tachometer plugged in or a jumper wire installed into that plug, the car will start while the starter is running but will die when the key is moved to the run position. This is an indicator of a bad tachometer because the current runs through the tachometer to the coil via the pink resistor wire in the run position.

On the tachometer plug is a [pink-(16A)] resistor wire that leads directly to the three conductor plug on the other side of the firewall behind the engine for the ignition coil. That three-conductor plug also has the wires for the temp and oil sensors. The purpose of the [pink-(16A)] resistor wire is to limit the amount of current to the coil.
Without that resistor wire your coil will get very hot and your distributor points will burn and cease to function.


Look at the top right of the ignition switch in the fourth picture.
There is a [green/red-(904)] wire tied with the [red/green-(16)], that [green/red-(904)] runs from the ignition switch connector and it goes past the firewall to the two-conductor plug at the alternator harness in the engine compartment and that [green/red-(904)] wire energizes the alternator circuit at the regulator. The [green/red-(904)] is hot in the run position.

Also at that two-conductor plug, the one that goes to the alternator harness, is a big [black-(38)] wire and that [black-(38)] wire is the missing wire in the schematic. It connects to the splice at the shunt where the small [yellow-(654)] wire is that runs up to the ammeter.


As I wrote this I found that the schematic shows that this [green/red-(904)] wire is tied with the [red/green-(16)] wire at the ignition switch connector from the main harness.
When I went out to my car to verify what I was writing, I found that there must have been a revision to the harness concerning this [green/red-(904)] wire or there is a miss print in the schematic.

On my car this [green/red-(904)] wire is tied to the same point in the fuse box as the big [black/green-(297A)] wire. And is not at the ignition switch connector.

Shown in picture five is the corrected location for the [green/red-(904)] wire as it is on my car. This may have been done to take some of the load off from that portion of the ignition switch.

I do not know when this was done but I would suspect that maybe on the 1969 and early 1970 models the [green/red-(904)] was at the ignition switch connector.

I do not have an early model harness to compare to the late model harness if that is indeed the case here. If some of you have your dash wiring exposed I would be interested to know if you have the [green/red-(904)] wire at the ignition switch connector from the main harness with the [red/green-(16)].
Please include if possible the build date for your car.

I have seen people pull their hair on power distribution circuits on the cougar XR7. I can understand why after my intense investigation.

I hope that I have presented an accurate analysis and not to difficult of an explanation of how the power/charge/start/run circuits work.

I did not focus on the XR7 alternator harness as that part is easily replaced with another. It just plugs in. I can if needed, let me know.

The standard cougar is wired very differently than the XR7 in many ways. This description of the wiring is not the same for the standard.
Wire colors and circuit numbers are different. This will not help a standard cougar owner.
I have focused on the XR7 mostly because I have only had XR7s.
I also find that a lot of people have the most questions about this part of the XR7.

Maybe some day I will write one up for the standard cougars as well.

I almost gave up on writing this due to it’s size but I have seen enough questions about the amp circuits
to make it happen. I hope this helps.

Mick Parsons.

Thanks Mick!

I for one have found this informative and very helpful in re-assembling my wiring. Kudos. :beerchug:

thanks Daryl.

I forgot to mention that a perfect source for the right color wire is from any ford product in the salvage yards of almost any year/model.
there are also some ford cars/trucks with ammeters, that will have the shunts and the fuse links all ready made in the harnesses.
they look the same but might have a heavy yellow wire instead of black, start at the solinoid and then follow it all from there.
I have taken whole harnesses out of cars and that has provided me with plenty of wire/fuse links.

mick p.

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