I am a car audio novice. I have replaced my head unit, in-door speakers, added an amp and 1 10" sub. It's a Pioneer head unit, Dual XPR2500 Amp, and the subis Rockford (I know, crappy equipment). The amp is bridge. My problem is that I can't seem to find a good spot to ground the amp, or at least I think that is the issue. I've sanded down a place that I believe is good for ground. When I start the car, the light on the amp is green. As soon as I turn on the stereo it goes red. If I loosen the cable and wiggle it a bit, the light on the amp will flash green briefly. Any ideas for me? I'm at a loss. Thank you in advance for any reply.