Back when I helped a friend build competition stereo systems, we always used the chrysler style wiring harness/plugs. It's petty easy to find the wiring diagram online. I'd just run new speaker wire, but you could use the existing wiring also. You'll have a constant power, remote power/switched, ground then the 4 speaker wires... they are same color per speaker with a tracer. Really not much different than installing an aftermarket head unit.