Originally Posted by Abysalone

You dont have to get the harness unless you have onstar. You do not need the factory headunit in the car.(maybe for onstar you do)

The factory headunit controls certain settings and options, everything but the door chime will work as normal without the relocation harness. The radio controls things light oil light reset, tire pressure reset, and lighting options like delays, etc. Nothing critical to the car working. Most service lights have other ways of turning them off like pushing gas 3 times while key is on, and engine off. That is pretty much what the relocation harness is for.

All you must have is the Impala to radio connecter, and run a wire from the fusebox for Acc. power. There is also a power drop under the passenger dash that you can take the power from. ZZP.com sells pigtails so no factory splicing is needed. And unfortunately you may have to cut the dash behind the radio. A small handled hacksaw blade works well here.