i have a 98 grand cherokee with an infinity gold system. this includes an amplifier for the speakers that is mounted beneath the rear seats, i believe. what i am looking for is an answer as to which wires should be tapped into to hook up a amp and subwoofer. or if there is another easy way to hook up a subwoofer to the stock system, it is loud enough and sounds good so that i don't want to replace the head unit, just want to add my subwoofer from my old car to it.