That's a W210 Chassis, right?

First thing that comes to mind is a fried wire - in this case probably a common ground. Check ALL your fuses, and give them a spin in their sockets. Those old MB fuses can look just fine when in fact they're not making contact on the ends due to oxidization.

If you give me some specifics of your car, I can probably look up the wiring diagram in WIS.

-tp