Okay I have a 1985 Z28 305 TPI whole car. Also have a 1991 305 Iroc motor, trans, rear, entire harness minus wires that were in the dash. But do have entire harness and ecm from that side.

Need to know what I need to do to swap this into the 85. ECM is bad in the 85, motor smokes a bit, trans is shot, so swap is happening. ECM is only like 55 bucks but if I can use the 91 free is better.

And when I say harness behind dash I mean like to heater controls, cluster, etc they didnt match whatsoever so I didnt see the point in getting them.

 

If you only have the 91 engine harness, you'll need to make a number of changes to the wiring harness to make it plug into the 85, the wiring changed significantly in 90, though it will be worth the changes.