Strange electrical problem
 

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?

Every operation of that car is computer controlled!

You need to have the car scanned for problems. Are BOTH batteries in good condition?