Color Wiring Diagram FINISHED

[70gmc4d]

Originally Posted by boundstaffpress

V8 engine and cab


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I don't see the three wires to the trany. I see the one green and one black to the reverse switch. My 70 GMC has three wires, dark green and light green to the switch and the black wire I just assume is a ground. But you know what they say about assuming. Thanks for the diagram it helps a ton!

[chuchito]

I have a 1972 GMC suburban, and the wiring is driving me crazy. The diagrams I found on here look similar to what I see under the hood but not exactly. Also, I don't see the blue wire that is supposed to be to the oil pressure on my harness but my guage cluster does have a oil pressure guage. The engine harness actually only has 5 wires. I unplugged it and looked at the female plug on the firewall and it also only has 5 inserts. The five wires I have are the tan, dark green, purple,pink, and brown with white. Can someone chime in?

[70gmc4d]

Originally Posted by chuchito

I have a 1972 GMC suburban, and the wiring is driving me crazy. The diagrams I found on here look similar to what I see under the hood but not exactly. Also, I don't see the blue wire that is supposed to be to the oil pressure on my harness but my guage cluster does have a oil pressure guage. The engine harness actually only has 5 wires. I unplugged it and looked at the female plug on the firewall and it also only has 5 inserts. The five wires I have are the tan, dark green, purple,pink, and brown with white. Can someone chime in?

My 70 GMC has a mechanical oil pressure gauge that is plumbed in the block next to the distributor. And the 70 gmc has 4 headlights up front.

[chuchito]

Originally Posted by 70gmc4d

My 70 GMC has a mechanical oil pressure gauge that is plumbed in the block next to the distributor. And the 70 gmc has 4 headlights up front.

Maybe that's how mine is too. There is a metal line that looks like it would go next to the distributor.

[TOYDOC]

Thank you for taking the time to make a diagram like this! if possible could you e-mail me a copy at ctoydoc@gmail.com

Thank you!!

[70gmc4d]

Originally Posted by 70gmc4d

I don't see the three wires to the trany. I see the one green and one black to the reverse switch. My 70 GMC has three wires, dark green and light green to the switch and the black wire I just assume is a ground. But you know what they say about assuming. Thanks for the diagram it helps a ton!

Just a heads up I'd anyone else had the same issue. I did ground the black wire to the fire wall and when I fired up my truck this weekend the backup lights work awesome.