I have a 1998 Expedition Eddie Bauer and I don't have a 8" subwoofer in the rear panel anymore. It was removed before I bought the vehicle used. I am trying to hook up a 12" sub instead but the wires are cut and theres an extra plug in the back. The two wires are green with a blue stripe and black with a green stripe. What are these? And what is the extra plug for?And is there another amp back there too?I need help thanks