68 XR7 Ignition wiring issue

I replaced my ignition coil while working on my engine refresh. Everything else has been mostly completed so wanted to her fired up and running for the first time. Went to turn the key and could not get it to fire. Checked all plugs again, wires are all correct, points set, disti set. So started looking at the wires to the coil. We put a volt meter on the hot wire from the ignition switch expecting to see power but didnt when the key was turned. So we disconnected it and ran a wire directly over to the + term on the battery and she started fine!
So, not being a mechanic or to good with electrical probs I need to figure out why that wire is not getting power from the switch when the key is on?
It is a red wire with a green stripe and 1 of 3 that come out the top right of the fire wall. The other goes to the Neg. Terminal on the coil and the third to oil sensor below the coil.

These are all part of the main wire loom under the dash before they split out to the ignition switch.
The strange thing is that it worked when I brought it home. Am I missing something I might have disturbed under the dash working on other things?

Ug, not sure how to rectify this as it seems pretty straight forward.

Much thanks,


Do you have a tach, and if so, is it plugged in? It has to be to get the car to continue to run. That line has 12V when the key is in crank, coming from the starter solenoid second (further back) position. That will allow the engine to catch while cranking, but once the key has gone back to RUN, the ignition switch takes over, which is why the tach needs to be connected.

The three wires coming out of the firewall are coil + (red/green), water temperature (red/white) and oil pressure (white/red). No wire attaches to the negative side of the coil from this harness.

What Midlife said. Sounds like the water temperature sender and coil negative are swapped

Midlife, thank you for the reply. Yes I do have a tach which is in a box with the rest of the whole dash cluster and parts! Your answer explains why it worked before and not right now as I haven’t replaced my gauges yet. So not sure if I can hook it up temporarily or not? I was not aware of the fact it was wired that way so I appreciate learning that.
Sounds like I misspoke on the wires and will go back and just verify I have everything correct there too.

The tach leads are male and female lugs so you can simply plug them together to bypass the tach.

Perfect, thanks Yorgie!

I checked and my wires are correct. I haven’t connected the two for the tech yet but will report back when I do.

Like Yorgie said - Just plug those two wires into each other and the car will operate without the tach.

Yorgie, I was looking at my cluster wires. I found a green wire that has a m/f connection to a green & yellow wire that has an unconnected male plug from the cluster strand.
Then I found the red/ silver wire with a red / yellow wire both connecting to a female connector which is connected to a green/yellow wire with an open male connector from under the dash.
So it would seem like those two male/female green & yellow connection would be it?
I did connect them and when I turned the key one click I got smoke from the main plastic plug connection for the whole cluster run! It was just for about a second till I turned the key off so one of these wire connection can’t be correct but I did see an obvious alternative?? Can try to post the pics I have for those.

I did look at my book showing the electrical drawings but was not able to get the wire colors I need to connect together. It has been a long time since I pulled all that out and just don’t remember them all.

If my memory is correct, one of the wires is the pink resistor wire and the other is red/green. The pink wire changes to another color at some point but ultimately connects to the + side of the coil. I think the red wire comes from the ignition switch. Someone with a wiring diagram handy can please confirm this.

Can you assist with the colors of those two wires on the cluster run? My gauges are packed away and it has been a long time since I removed them.

Thanks much!

I found this:

What Randy said. Here’s the Ford ‘diagram’ of a factory tach installation

Not shown but important: The wire between the tachometer and the coil includes the ‘pink’ resistor wire. The OEM tach will not function correctly w/o a

I guess the pink wire with a red connector attaches to the Black wire from the tac to go to the coil +.
So then the red wire from the tac would go to a black wire?? I found the pink one but not the other.

I believe that’s correct- black wire from the tach (which should have a female plug end) goes to the coil through the pink resistor wire which should have a male plug. Look for a red/green wire from the ignition switch harness that has a female plug- it should be hot when the key is in the start and run position- as I recall it’s fairly short and it’s probably hiding somewhere behind the ashtray.

Yorgie, just when I think I making progress I got a wall! The above diagram shows the Black wire from the tac with a male connection. My tech black wire is female and about 3" long. The pink resister wire has a male connector but had a 3" tail connector that is a red wire with both m/ f connections, to bridge I guess. But why would they have a red wire bridge between the pink and black wire?
Also, the wire connected on my coil + is red/silver, not pink. The pink wire runs into a look on the left side of the wiper motor, not the ignition switch loom.
I did find a red/silver wire paired with a red/yellow wire with a female connector. That red/silver wire is the same as I have coming out of that 3 wire group in the firewall to the coil area. Is that correct? If so I don’t know where the pink wire even goes unless it changes color at another connection i can’t see.

Thanks again,

Alright, quick update. Mystery solved. Found this basic video which shows how the pink wire connects to the tech and the run of two red/green (I said silver) connect to the tech and how to bypass the tech to start without your tach. Please let me know if the link I copied and pasted works for you.

WCCC shows a red connector in front of the pink wire in the photo for their replacement harness.


Much thanks,

The harness in the video is obviously for a mustang but that’s the concept. Sounds like you have the resistor wire. Now just hunt down the other wire. I believe it’s the only single prong female plug in that area of the dash.

Yes, agreed but I found through my research that the tech wiring in our Cougars is the same as the Shelby so it was helpful. What was important to me from the video is that red wire I was looking for had a second red wire with it and they both run into the same female plug! I was looking for a single red/green wire with a female plug so learned something new again. Anyways I easily found that so all is well to get those two connected to fire up this weekend. Also, it was good to know the pink wire has a solid red short connector on the end and that it eventually ends up changing back to the red/green which is the color when it actually attached to the coil +.
Thanks for you patience as this is my first rebuild.

I plan to attach a few photos on this thread for the next guy that needs the info.