Just upgraded the stereo from the stock factory radio. I've noticed that the fader isn't working, and I didn't think to check that prior to the upgrade. When I set the fader for the rear, there is no sound. I'm suspecting that all six speakers are wired on the front channels. Going to attempt to trace the wires to see if I can prove that out, but am curious - has anyone else encountered this? My unit is a 2004 GS EnduraMax class C on a chevy 5500 chassis.