1999 mountaineer radio help

ok… i want to put a aftermarket headunit, and my amp and subs into this truck. problem, it has the premium sound package, so theres a amp in back, i got the harness,s that are supposed to bypass the amp, but theres still 3 harness,s that go into the radio. i bought the harness thats supposed to work but it does not fit on any of the 3 harness,s that come from the dash,i pretty much need a how to install for dummies, on how to wire a system in this type of vehicle, ive never had a car with the premium sound nor put a system in one so im a newb at this

thanks steve

http://installdr.com/QuickWiring.html

metra 5517 or 5701 will work. Hook up the blue wire coming from the harness to the remote lead from the head unit. this will send 12v’s to your factory amp.