I have an 88 Iroc 350 tpi. I'm in the process of swapping over to a holley efi unit & stealth ram/ 383 new motor. The unit can run the fuel pump, fans, and tcc lockup. Along with the engine.

I've completely removed the harness from the driver firewall to the interior. I would like to keep the gauges working, ac, alt, etc working off the factory section of the setup, but remove the ecu and all the wires that run the engine. That way I can have the ecu & wiring to run the 350 tpi in another project and so it will look like a cleaner job.

Some threads say you have to cut and splice to do this others say they are separate and can be pulled apart. Does any know if the section of wires can be pulled apart it would make sense since everything connected to the ECU shouldn't be needed with the holley or is their something important I'm missing?

Also I'm wondering about where two plugs. The first is the plug connection next to the ecu what all does that feed. and the 2nd is a 3 wire connection where from the main harness to the a/c feed lines coming through the firewall(to the right of the heater box)

This are the pics of the two connections in question

Splitting the power/gauges part of the harness from the EFI part without destroying one or the other is quite challenging and time consuming, but not impossible. Remove the loom/tape from the C100/C207 and locate a pinout for each for your particular year. Tag each wire. Several will be free just with the loom/tape removed, such as coolant gauge, power wires etc. Some will not and need to be cut free. This is where an understanding of the circuits is key

An easier solution is to find a junk V6/TBI harness matching your year and cut the EFI system off without regard to saving it. I wrote a thread detailing the process in the LS1 swap sticky "3rd gen harness prep"

Splicing the aftermarket system on is made simple from there

I think I've got it took about 5-6 hours to them apart grounds , power in run pos wires, relays tie into both sides, etc.... Once I get everything hooked up and if it works like I want ill try to post a detailed thread to help others out on a similar projects

I removed the ECM harness in 20 minutes on my car. I'm not sure if the previous owner took apart the ECM harness from the other harness, but I was able to pull it right out without a problem. Most of the wires going to the engine were cut since the engine had a a Holley carb, intake, and new distributor.

Here's my ECM harness when I took it out of my car. Seems like it was a whole seperate harness.


The connectors next to the ECM are for power and the check engine light in guage panel along with some other things I'm forgetting. You can cut all of that out though.

Early cars like that do have separate harnesses for EFI and gauges. 85+ EFI are completely integrated