I receantly bought some used stuff from a friend of mine, 2x12" subwoofers, VDO Dayton 4x150W AMP and 2 Sony xplod frontspeakers. I've wired everything right but there is a problem. Everything works well when the car engine is off but as soon as I turn the engine on the subwoofers won't play. I've connected only the subwoofers to the AMP and the speakers to my stereo. Need help, I've desperatly tried to fix this. Oh and everything worked in my friends car even when the engine was on.