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-   -   Ignition switch wiring help (https://6066gmcclub.com/showthread.php?t=51206)

Jethro September 7th, 2021 12:11 AM

Ignition switch wiring help
This morning I set out to do a simple ignition switch replacement on my 64 I1000. Then I found out it ain't so simple. The wiring on my truck has been "fixed" by way too many previous owners.

Here's what I had.


Here's what I have.


The brown and white wire was on the acc. post of the old switch. Is that right? It's a solid tiny wire. Resistor wire? The other end goes to the alternator and the Gen light.

The dark green wire was just hanging there. Where does it go? The other end goes to the instrument panel temp gage and another green comes out and goes to the temp sender.

The wiring diagram I'm looking at doesn't match reality.

Jethro September 7th, 2021 12:23 AM

Re: Ignition switch wiring help
I'm also wondering if my coil is wired right.
As is the pink wire goes (among other places) to the 6 pin connector on the right firewall. From there it changes to a black wire with a cloth insulation and goes to the starter R. From the starter R a yellow wire then runs to the coil +. It runs but, is that right?

Thanks in advance for any help I can get.

AZKen September 7th, 2021 10:05 AM

Re: Ignition switch wiring help
After many years and many owners, you can't trust wire colors sometimes, so be sure they go where indicated.

Ignition switch wiring per 1965 GMC diagram: I do not see a legit 1964 GMC diagram.

1. Red to terminal "BAT. This is an "always hot" battery source.

2. Pink to terminal "IGN"

3. Violet to terminal "SOL"/"START". This wire comes from solenoid terminal "S"/"SOL"

4. Brn/Wht to terminal "ACC". This is part of the charge light (tell tale). It comes from the Voltage reg "L", goes thru the right side 6 pin, comes out as two wires. One BRN/WHT and one BRN. Brn/wht to ignition ACC as described and the Brn goes to cluster "G" which connects to the Gen Light thru the flex print.

5. A brown wire from "ACC" to fuse panel. The terminal it goes to has another brown wire on it that is jumpered to another terminal. Don't see another other way to describe. No number on fuse panel given.

The Dark Green shows on diagram from temp sender thru right side 6 pin, then to cluster "H" which connects to temp gauge thru the flex print.

Yellow from coil pos to "R" terminal on starter solenoid. Resistance wire from "R" to right side 6 pin. Comes out of 6 pin as a pink to Ignition switch as described above AND to cluster "E".

It's up to you to sort out the wires and be sure they go per diagram. If the colors match, all the better.
Report issues/questions before powering up. You are only using 4 out of 5 ignition switch terminals. I believe the 5th is GND, right?

Jethro September 7th, 2021 04:10 PM

Re: Ignition switch wiring help
Thanks AZKen. Looks like I'm all good thru #4 if I connect that brown/white to acc. Which is how it was. Just wasn't sure.

#5, brown fromacc. to the fuse panel doesn't exist on my truck. Maybe the dark green is doing its job? I'll have to trace that one again after work.

I've looked at every diagram I could find on line. Including the wrong year and even a couple cars.
The only one I found showing a dark green to the ignition switch was a 64(?) Chevy II. That showed dark green to the GRD terminal.

And, yes, there is a GRD terminal on my new switch.
Does that ground the switch? Or just give a spot to ground other stuff? The switch should be grounded automatically to the metal dash, right?

I'll retrace the dark green after work and go from there.
Thanks again.

AZKen September 7th, 2021 09:02 PM

Re: Ignition switch wiring help
According to 1965 GMC diagram, the browns are part of the Gen Light. The green is temp. The GND terminal is not used.
Chevy is sometimes the same , sometimes not. Wire per function, not color. That's why I explained the "to-from" as well as the color.

gmcjuniorvan September 8th, 2021 01:45 AM

Re: Ignition switch wiring help
1 Attachment(s)
1964 GMC I1000 I1500 I2500 wiring diagram.

Jethro September 8th, 2021 03:28 AM

Re: Ignition switch wiring help

Originally Posted by gmcjuniorvan (Post 74623)
1964 GMC I1000 I1500 I2500 wiring diagram.

You da MAN!
Thanks. That actually looks like it might be THE diagram I've been searching for. At least it shows the green wire I've been chasing just like it is in my truck. Goes to the ground prong on the ignition switch.

As of now I have pretty much the whole harness unwrapped in the cab. Figgered I'd try and make my own diagram. I was pretty sure that green wire had to go to ground. Now I know for sure.

I'm glad I went this far tho. I found several more electrical gremlins in the dash. I'm gonna chase the wiring all the way from stem to stern. The main objective here is functional reliability.

AZKen September 9th, 2021 02:01 AM

Re: Ignition switch wiring help
Don't think that green wire goes to ground. The ground terminal is if you have a hot light instead of a gauge. Unless you have both. Do you have an actual ACC position on your switch. Like full CCW?
At any rate, that is not important. The green wire that is important is the one from the temp sender to the gauge. But you said you were going to trace the green wire(s). The 64 and 65 diagrams are basically the same. Slight changes.

Jethro September 9th, 2021 01:15 PM

Re: Ignition switch wiring help
I do not have a hot light. I do have ccw acc. on the switch.
Sure looks like green goes to the ground terminal on that diagram.
I did trace the whole wire. And all the rest.
Here's my rendition of the green circuit.


gmcjuniorvan September 9th, 2021 05:37 PM

Re: Ignition switch wiring help
I think the dark green on the ignition sw is for when you turn the key to ACC the temp gauge would go to H. On a chevy the hot light will come on. This is to check the chevy light. If you want to check the gauge use it. I would not use it. If you left the ACC on for some time you could burn out the gauge. Just tape it up so it will not ground out.
If you look at the 4 pin panel connector on the wiring diagram you will see 20 L.GR 36 your truck could have this wire itís for the chevy cold light.

One more thing, when you rewrap the wiring harness donít use electrical tape use OEM factory wiring tape it will not stick to the wires. When you have a metal body clamp around the harness wrap Teas 51036 tape around the harness, itís a cloth tape that has a high abrasion protection

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