I am not familiar with your specific vehicle, but all cars share some common electrical issues. The symptoms you describe are indicative of a bad "ground" somewhere in your wiring. I'd look at two areas for possible corrosion. Check the cable which runs from the battery negative post to the car frame, particularly where it bolts to the frame. Also check where this negative cable bolts to the engine itself. The bolts where these cables get connected corrode, especially the one near the battery. Have a real close look at the cables themselves, as the copper corrodes on the inside and often you can't see the problem under the insulation. Inspect those short "jumper" cables which go from the engine to the frame. Mercedes often runs return circuits (grounds) to a common tie block, particularly those in the instrument and dash area. Inspect your fuse blocks for corrosion. If you still have aluminum fuses, consider the newer brass type. Beyond these suggestions, you'll need a volt / ohm meter to measure voltage and resistance to ground at various points in the system.

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