Most of the time on Mercedes the Windows stop working due to spilling your drinks and food on the switches, you may have to remove the switches take them apart carefully and clean all the debris out of them. I am giving you a component location to the window relay make sure it is working let me know what you find.
Convenience Control Module (1)
Under left side Of Rear Seat
Convenience Control Relay (K24)
Rear, Left Side Of Engine Compartment In Fuse Box
Front Door Pin Switch
Appropriate Door Jamb
In Engine Compartment
Power Window Switches
Center Console & Appropriate Rear Door
Rear Window Safety Switch
Center Console (1)1990-95 vehicles are equipped with a 4-power window system.
Tuesday, October 5th, 2010 AT 11:38 PM