I have a 2007 king ranch screw with the factory sub and amp set up. It sounds great when it works, meaning that the sub works sometimes and then will just go off?! I assume the amp is going out. Obviously the easiest thing to do would be to replace the factory amp so my first question is where is the best/cheapest place, other than ford, to buy one? second question is how easy/difficult is it to install an aftermarket amp in its place? is there a way to plug the aftermarket amp into the factory wiring harness? thanks guys for your input!!