I got a 92 mercury sable LS wagon that I've halfway installed a new head unit in.. I say halfway because I got all the wiring done up and plugged into the factory harnesses, turned the car to give it a try but got nothing. The head unit turned on just fine but I got no sound. I've installed all new speakers all the way around but I wasn't sure if I am supposed to by pass the factory amp or not. Any advice is much appreciated... I just want sound in the ol' girl again.its been to long.