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Years ago I replaced the stock idiot light dash cluster with the proper Ford OEM instrument cluster from a GT. The butt connectors are where I spliced into the red/green coil wire for the tach. (Not how I’d splice today but it works). The tach has always worked during this whole months-long odyssey even though that wire has had 2 different voltages on it. FWIW.
That comment is worth a lot !!
The red and green coil wire attaches to the coil +.
A tach is normally connected to the coil -.
Please look at picture 2 in post 213 at where the brown wire meets with the red/brown wire. We definitely need to/will come back to this. Please make a note.
The red and green coil wire attaches to the coil +.
A tach is normally connected to the coil -.
Please look at picture 2 in post 213 at where the brown wire meets with the red/brown wire. We definitely need to/will come back to this. Please make a note.
Noted; downstream at the flat connector.
FYI regarding the tach wiring: I’m a longtime member of ranchero.us. That’s the same website we’ve both found and then posted wiring diagrams. The same member that provided those diagrams (72GTVA) has a lengthy thread that discusses the similarities and differences of the various sports (i.e., GT) gauge clusters that Ford produced during the 1972-1979 model years, hence my prior comment about my using the proper one since there are model year groupings. Mine has the correct part number. Anyhoo I printed that thread when I switched-out my panel in about 2008 and still have it. Here’s a picture of his instructions about tach wiring.
Assuming your answers to post 226 are yes, please do the following :
Using picture number 2 in post 219 as the reference, please put the 3 cut wires to the right side of the valve cover.
Please put the orange,black with blue dots, and black wires to the left of the valve cover.
Put the remaining wires down the middle of the valve cover and post up a pic.
Or, if there are only 7 wires in total, just confirm that all 7 have been verified.
Then, please check which of the yellow wires connecting to the ICM plug feeds to the starter relay. (Yellow one or yellow with blue spots one, per page 1 of the recent attachment.)
Then follow the other yellow one and see exactly where it goes to.
You might have to unwrap and follow wires all the way to the ignition key after all.
Why ???
Because we need to thoroughly check what we have/have not, so as to correctly supply the coil with 6v in run, and 12v in start.
Because we have cut wires, 1975 bits, and the wiring diagrams aren't 100% helpful.
Ah, your tach wiring is a new one on me. Can't argue that ! Thank you for the diagram.
Mine has only one wire, to coil -, but it is not OE.
I'm off to bed now and will check in again with my morning coffee.
We hadn't got as far as picture 3 in post 219 with regards to comments. Arrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrgh.
I've just seen that the coil + red with thin green wire actually connects to the brown wire at the connector, and that brown wire connects to the pink wire at the ICM.
Ok, that entire circuit is 12v. Haha, we know that already.
Are the brown/pink wires that you modified for the tach, connected to that red/green wire ?
If yes, please post up a photo showing the connections. (Not visible in previous photos.)
Also, if the green coil - wire still reads 12v, we have to check out why. (I'd forgotten about that.)
Moving on swiftly, the next job is to follow the wires from the red and white ICM wires all the way to wherever they terminate, noting any and all splices etc.
In picture 2 in post 219. Is that an unconnected vacuum pipe, and if yes, where is it normally connected ?
That goes to the brake booster. I disconnected and moved it to have better access. Same for the HT leads on the dizzy as well as some electrical plugs.
We hadn't got as far as picture 3 in post 219 with regards to comments. Arrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrgh.
I've just seen that the coil + red with thin green wire actually connects to the brown wire at the connector, and that brown wire connects to the pink wire at the ICM.
Ok, that entire circuit is 12v. Haha, we know that already. Both statement above are correct. Also, the pink wire connects to nothing in the ICM plug. Also, critically this wire should be resisted to 6v in Run, and it’s intermittently and predominantly 12v.
Are the brown/pink wires that you modified for the tach, connected to that red/green wire ? I didn’t touch either. The tach is spiced into the red/green in series with the coil, on the firewall side of the connector. The brown-turns-to-pink wire is on the engine side and goes to the ICM.
If yes, please post up a photo showing the connections. (Not visible in previous photos.) The answer is no but I will post detailed pics of the various connectors.
Also, if the green coil - wire still reads 12v, we have to check out why. (I'd forgotten about that.)
Moving on swiftly, the next job is to follow the wires from the red and white ICM wires all the way to wherever they terminate, noting any and all splices etc. The red wire on the ICM turns into yellow/blue at the connector. The white wire turns into yellow. (The yellows were probably actually white at one time but no more, they look yellow so that’s what I’m calling them at least until we run into a true yellow wire somewhere, lol!). More below in the main post.
I traced the ICM red (yellow/blue) and ICM white (yellow) back to the harness connectors near the firewall.
The yellow (Start) wire goes into a factory-loomed wire harness that goes across the firewall that would lead to the starter solenoid though I didn’t see a wire that color on the solenoid.
After going through a couple of connectors the yellow/blue wire (Run) goes into a harness that disappears under the steering column that would seem to go into the passenger compartment though that’s not confirmed. All wiring from the ICM to the firewall is factory loomed.
I’m posting several pictures to hopefully provide better visualization:
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