I'm thinking on replacing the entire Fiero harness with the GP harness, though it may be easier to buy a Firebird and use the harness from that to start ( then I can also have the dash to swap in)
I bought the Fiero with more electrical problems then I realized. it started and ran, but would blow fuses and act strangely ( headlights up and down, wiper speed erratic, radio blowing fuses, intermittent brake light function.. etc) which made me dig into the harness a bit where I discovered damage from rodents, poorly placed zip screws, and what i assume was an after-market stereo install that went wrong and was mishmashed back to the factory radio.
My original plan was to just 3800 swap and drive, but now that its winter i might as well fix everything I can.