I've got a 86 IROC, 305 carb. I'm going to pull the motor (its had a bad life) and swap in a 350. The wiring under the hood has been butcherd over the years from car alarms, melted wires and rewired fan controls (using speaker wire). Basically the wiring harness under the hood is unreliable. What do you guys usually do in this situation? I don't see any wiring harness for that year via aftermarket. I'm pulling the smog junk and the roch carb. so many of the electronic do dads will be a dead end with the new motor. I do have AC, it works so I'm keeping it.

 

You are about to do what I am just finishing up. I have an 87 that had a 305/carb. I pulled that and threw in a built 350/carb. I put the engine in 2 years ago, but the thing was just never right after that, I'm talking about the wiring. So I am just finishing installing a Painless wiring Harness. the 18 circuit one. So far so good. No complaints. I should be finished this weekend with it. Like you I kept the A/C. The Painless kit has most of the wires for everything. I had to keep some old connectors and A/C wires to make everything work.
Let me know if u need any help. Where do u live?

 

I'm in Colorado. Painless wiring must have some pain associated with installation. Your rewiring the entire car with this kind of kit? I was wondering about just a engine harness. How do you deal with the computer? I've had to fix several problems with the engine wiring due to age etc. I'm guessing if I put that motor in I'm still going to be fixing electrical issues unless I replace the whole wiring harness under the hood.
I'd like to hear more details and understand how you dealt with the computer controls. I'd also like to hear your estimate in hours for doing the work. Bet it isn't easy installing that harness when it is a more general harness rather than being specific to our particular model/year.

 

I tore out anything having to do with the computer. Its all run through the Painless kit. I believe they do sell just the engine section, but I'm not sure what that all consists of. Our cars have two different wiring harnesses in the engine compartment. One that comes up from the passenger side bottom by the door and one from the firewall on the drivers side. The one on the passenger side runs right to the computer. The one on the driver side runs to the fuse panel and gauges, with a few exceptions. If you leave the computer in their it will never work properly cause you wont have everything hooked up. Why do u want to leave it in? What all have you removed from your car and what do u plan on keeping?
As for the kit. I thought it was laid out very well. All the wires were marked and grouped. I had to do a little re-grouping of them cause I wanted to route them my own way. But basically all the wires are there for the whole car. You will have to run some of your old wires for the accessories such as A/C and stuff. They just have the power wires for the accessories. You have to use the stock harness for the rest of the wires, if you understand what I'm saying. I have an 86 and 87 shop manual with all the electrcial diagrams so that maid it 10 times easier. I wouldnt even try it with those! I have been working on it for prob 3 weeks on and off. I'd say you could do it in a week. It is a big job.

 

I believe there are three harnesses running into the engine bay. One comes from the computer, then through the pasenger fenderwell. The 2nd comes from the fuse block on the driver's side, and the 3rd is a small harness that comes in below the HVAC. Your best bet would be to get what you need from a wrecking yard. 3rd gens are very plentiful. You would probably be money and time ahead by getting the right one.