Help, my hatch has a strange voltage surge. The voltage reads 14.0 volts when I drive and then when I turn the lights on it drops down to 13.0-12.5 volts and then goes back up to 14.0v . Also when I turn the windshield wipers on the voltage drops down to 12.5v and keeps going down the longer the wipers are on. This all while the car is on. When I rev the engine it jumps back up. HELP!