85 GMC Engine Wiring Questions

I bought an 85 GMC C25 and am in the process of swapping it all over to a SWB C15 frame. Truck has a 350 "M" with THM400 all original.

Questions I have on engine wiring.

1. I found four wires close to the alternator that were previously cut. The look pink/black x2 and 2 solid black wires. Smog (A.I.R.) had been removed prior. I assume these wires went to something on the emissions but would like to know.

2. Blue wire from engine harness. I believe this goes to electric choke on the carb. Not sure.

3. Pink/Black wire that comes out of harness next to blue wire - where does it go?

Thanks!

My '87 also had the pump removed, and there is a two-wire sealing plug laying on that side of my engine. The pumps do have an electrical connection to them. I can't recall exactly what colors they are though.

Looks like a pink/black & a brown.

the second photo is a zoom in of the first.

AIr diverter solenoid, possibly egr,
The brown leads to your ALDL under your dash. as well as an output from your ECM. That wouldnt be good to have ground out for sure, but it means your system may be looking for the AIR depending on how things are setup.

AuroraGirl said:

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the second photo is a zoom in of the first.

AIr diverter solenoid, possibly egr,
The brown leads to your ALDL under your dash. as well as an output from your ECM. That wouldnt be good to have ground out for sure, but it means your system may be looking for the AIR depending on how things are setup.

You must be registered for see images attach

Click to expand...

Ahhh, "Air Diverter Soleniod", that's good to know!

Thank you for the diagrams. If only I could make sense of them. They don't seem to match my truck as it was a 2500. I have a pink/black coming out of the harness next to a blue wire. I think the blue wire goes to the choke. Not sure where the pink/black goes. Then I have the additional two pink/blacks with two black wires that come out of harness with alternator wires...these were cut. Not as worried about where they ran as I am no longer using the smog stuff.

scape said:

Thank you for the diagrams. If only I could make sense of them. They don't seem to match my truck as it was a 2500. I have a pink/black coming out of the harness next to a blue wire. I think the blue wire goes to the choke. Not sure where the pink/black goes. Then I have the additional two pink/blacks with two black wires that come out of harness with alternator wires...these were cut. Not as worried about where they ran as I am no longer using the smog stuff.

Click to expand...

Dontcha just love it when a "hacker" goes into a harness and cuts everything loose.. As to that pink/black wire. It runs all over the place providing ignitioon On power for lots of stuff.. Starting with the ignition hot circuits, ignition ON voltage is used to feed the electric choke. A wire that basically is hot with ignition on goes to an oil pressure switch. (ON with pressure, OFF with no pressure) This wire is pink/black. From the other terminal on that switch, a blue wire goes to the choke,,, If your choke wire is hot with ignition ON but engine isn't running, your choke circuit is wired wrong. That oil pressure switch is located in the block just above the oil filter. It is a totally separate circuit from the oil pressure sending unit for the gauge.

Appreciate this feedback. I will dig into this tomorrow. Mine does not have the oil pressure switch in that location, but is combined with the oil pressure sending unit at the back of the intake. Here is my harness and what I know goes where...or, at least think I know. Here is a diagram I put together.

I'm about to begin the arduous task of wiring up my Frankentruck. What was sold to me as a 1985 is actually an '81. (I had a cop friend run it to make sure it wasn't hot). Never have I ever seen a more effed up hack job on a wiring harness. I swapped in a SBC - fresh build with a carb - no smog related equipment at all. Block is from late '60s. Any advice would be welcomed. should I buy a harness for a late '60s truck or just make it up as I go?

Nardulli said:

I'm about to begin the arduous task of wiring up my Frankentruck. What was sold to me as a 1985 is actually an '81. (I had a cop friend run it to make sure it wasn't hot). Never have I ever seen a more effed up hack job on a wiring harness. I swapped in a SBC - fresh build with a carb - no smog related equipment at all. Block is from late '60s. Any advice would be welcomed. should I buy a harness for a late '60s truck or just make it up as I go?

Click to expand...

Is the accessory drive from the 60s or is it match? The 60s had a different approach to the accessories because of mounting holes and less things like AC being common, smog pumps, power steering was more optional. the water pump is usually different Long is common i think 69 and later.

What cube engine you have?