Order an installation kit from crutchfield. It will come with all of the wiring harnesses and VERY detailed instructions on how to get it hooked up correctly.
They cost about $20 and are car/system specific, so even a "car audio idiot" can get the job done.
If you can use a wire stripper and electrical tape, you can install a HU with the crutchfield kits.
BTW, it's
www.crutchfield.com. It does sound like they didn't bypass the factory amp, which the crutchfield instructions tell you how to do.
