3800SC Harness (Page 1/1)
Jlife MAR 23, 03:28 AM
If I want to make my 3800SC harness off the car, can anyone tell me what things I need to be careful of. Is there a certain length for wires that I may need to be careful of or can I just use standard harness wire as it came. Thanks

[This message has been edited by Jlife (edited 03-25-2023).]

Spoon MAR 29, 10:11 PM
I pulled my 3800sc from a 2000 GTP along with the entire harness's and the ECM. I separated the harness from the engine and mounted the engine on an engine stand. I'd planned on having the ECM in the car behind the center console so I used a piece of plywood as a bulkhead placed xx inches from the engine/stand. Mounted the ECM and drilled a few holes for the harness to pass thru.
The next task was stripping off the tape and sheathing from the engine harness. Since this engine was from an air conditioned and automatic car there were lots of unnecessary wiring to set aside. With the aid of a genuine factory manual I was able to isolate the required wires and delete the unneeded ones from the harness. I tagged every wire to identify its function and color. Wire length was more that adequate so no splicing was required. A word of caution, some of the wires within the harness closest to the engine had changed color along the way from the ECM. This was due to heat. So a yellow wire from the ECM appears to be a white wire at the engine so tagging is important.

Since this is a custom harness I chose to follow a path that was convenient and neat. The C500 harness was made with no issues as well as other connections for the speedometer, etc. I was amazed when I turned the key and the engine came to life. I give credit to Darth for his information and reprogramming my ECM.

http://www.gmtuners.com/fil...PCM_Fiero_wiring.pdf

PS: "A child could do it."

Spoon

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"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

Jlife APR 01, 09:07 AM
Thanks Spoon for that reply. I'll be working on mine this spring and the technique you mentioned seems like a plan. Thanks
Fie Ro APR 07, 08:40 AM
That is a good way to do it but if you are after a clean (hidden wires) setup it might be better to do it with the engine in place. It is hard to determine the needed length of a wire when it will be routed up/down left/right etc. In either case you might want to think about how you want to route the wiring to determine the best length, especially if the pcm is in a different location than in the donor vehicle. I made my harness mainly low around the enginebay and going to the engine where needed. Around the enginebay the wires will be covered and the Pcm is in the trunk. This way with all the routing I could only do it in the car.

Yes, tracing and tagging ALL wires may be a bit of work but it makes it way easier later. I put the function and pin numbers on each to have a reference to the diagrams.
Diagrams: You'll need the Fiero diagram, the donor engine/vehicle diagram and Ryan's/Darthfiero's diagram. Ryan's diagram is gold when putting everything together!

Remove unused wires from the pcm as per Darth's instructions.
Delete/rewire C500.
My donor harness was cut and I got a second harness. Both were incomplete but I could use enough wires to make them to the needed length and color. I was planning to use 1 or 2 multiconnectors between engine harness and pcm harness but I abandoned that idea when it appeared more complicated than I thought. Now I can disconnect or replace wires per sensor without tearing into the rest of the harness. Also the engine can be easily diconnected this way (I still need to put a clutch and flywheel in).
You might also want to do the fuelpump hotwire upgrade when doing the wiring. That's also on Darth's website.