I recently purchased a Pioneer XM radio for my 2004 E 500. I power it with the cigarette lighter adaptor. Since I started using it strange things have been happening with my electrical syst. The 4 way flashers and dome light go off when there is no-one in the car.This happens even once the sat radio is unplugged, once I have left the car for a while. A couple of tines it drained the battery. Any suggestions?