If it was me and i was keeping the fiero drivetrain, ac/heat ect I would keep the orginal fiero wiring. But in my case doing a motor swap it just made more sense to replace it with a new wiring harness.
The wiring harness I got came with a GM plug for the steering column so that was just plug and play. My power window wiring I also got a wiring kit off ebay for that to. It came with relays and just had to tap into my window motors and switches. Every thing else I had to wire, gauges, alarm, stereo, ect. I also made my own LS (microsquirt) wiring harness, my trans controller just need to be wired to the trans plug. I did a ton of wiring, but if I can do it- anyone can do it.