looking for help wiring 5.0 swap
Reply #3 –
You'll need to find the engine harness from an '86 5.0 Tbird/Cougar, unless my memory is bad and the '86 cars were CFI, in which case I'm uncertain what you'd want to do.
Don't try to modify the Mustang harnesses as they're not worth spending the time on, though it has been done. If all else fails, and you can't find the proper Tbird harness, use it as a last resort, but you'd better be really good with wiring.
You might even try an '87 or '88 5.0 Bird harness, but likely will need some repinning done, as well. Good luck.