Part of it depends on power requirements. If the new radio has a high output audio section, the old harness/ fuse may not be enough. So look in the destructions and see what the requirements are
Generally.......the two wire original plug has red--switched acc power, and orange--dimmer controlled dash lamps. You may need a constant power feed for the new radio memory, so you'll have to run a wire over to the fuse panel "hot" buss
