You can actually use the harness off the factory unit. Simply cut the wires coming out the back of the factory radio but be sure to leave enough wire to add connectors to the factory radio wiring if you ever have to re-install the factory unit in the future. Purchase a pack of bullet connectors from your local auto parts store. Crimp the male end to the wire (leads) coming from the aftermarket unit and the female connectors to the wires (leads) of the harness you just removed from the factory unit. There are a total of twelve leads you'll have to crimp (six plus six). If your aftermarket radio has pre-amp outputs, simply plug them in (that's if you're not adding aftermarket amps and doing a total rewire). The Viper has two sets of pre-amp connections for two amps - one for the front speakers and one for the rear 6.5" subs.
As I mentioned before, if you ever need to re-install the factory unit, simply crimp the matching connectors on the leads coming from the factory unit.
A wiring diagram is listed in the service manual which has the wire colors. You need to make sure to match the correct wire from the aftermarket unit to the harness.
