I have an 86 Iroc that has an 89 Firebird motor. When the motor was changed they also changed the harness, for what reason I do not know as I thought that they were all the same? The car runs and drives but the nothing is hooked up on the inside. The Firebird inside harness is completely different and its about to drive me insane. I have tried several manuals to help me sort it all out but to no avail. My question is can I just switch backt to the Camaro inside harness? Unscrew the plug at the firewall and just switch? I have the old harness all except of course the inside! So i will have to go get one but I can handle that if it will work. If I can't just change the inside harness is there any reason I can't put the Camaro harness on the firebird engine and then switch the inside harness? Any help would be of great benefit to me! I am about to give up.
THANKS

 

Not sure if the harnesses are the same between the 86 and 89 motors, I guess if they were both MAF TPIs then they should be.
Most of the wires in the harness for the sensors go into the ECM except a few that go to your dash gauges, like oil pressure, and maybe fuel level if thats even in the harness. While others are shared between the ECM and the dash gauges, such as tach, speed (VSS), temp, etc..
Those sensor wires that go to the dash should have a single connector with all of them in it that connects to a connector coming from the dash. The connector should be about a foot or two from the ECM's main bundle of wires coming out of the ECM.
Maybe that is not hooked up and thats your problem.
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If the connector is not there, I don't know of any reason it would have been cut off. You may want to find out why they didn't use the existing harness you had alreay, there may be some reason there. At least this is the way my SD TPI harness was.