Bought my crossfire used. It had an Alpine head unit in it-no bass at all. I recently decided to purchase a factory head unit to put back in. Whoever previously installed the aftermarket Alpine had cut out the factory wiring harness that attaches to the back of the head unit. So I had to order a wiring harness. I now have everything hooked up except a pair of blue and a pair of yellow wires, which according to the diagram, run to the amp. Where do these hook up to, into the harness. I currently have no sound/bass from the rear