Could be a harness issue. My drivers side rear door window has been unplugged from the main switch since I found out the blue wire was giving 12 volts to the instrument cluster when i use the switch. It took out my cluster. Look inside the rubber accordion thingy in the door hinges. Maybe its just there. Mine is somewhere between the hinges and switch. I havent fix it yet.

__________________
'85 300D Cal 280,000 miles
'14 GLK 350 60000 miles