I have recently purchased a 2011 F150 lariat and the previous owner had a sub or amp or speaker under the back seat. There are 5 wires that come from the carpet where the old system used to be. The wires are red, green, black, and two rca cables. I believe the black is ground. The red is the power wire. And the green goes to a sub controller dial in the front. What kinda of speaker/sub would work with this setup?