When purchasing a head unit from Crutchfield they provide a wiring harness adapter kit for free, it's worth it's weight in gold cause you don't then have to cut into the stock wiring harness on the car at all.
You just take the harness connector that comes with the head unit and solder (or crimp is ok too, although solder is better) it to the adapter provided by Crutchfield. You vehicle connector then plugs into it, easy stuff.
Only problem is if you want to maintain any steering wheel controls if you have them. That's another story... lol
