You need the other part of the wiring harness that connects to the Ford adapter. Go to a car audio store and tell them what kind of car you have and they should be able to hook you up. Shouldnt cost more then $10 or $15. If you had a premium audio system you might also want to consider bypassing the stock amplifier, your system will sound much better if you do. Some audio stores sell the bypass, but you can definately pick it up at
www.crutchfield.com. 
