I've seen strange behaviors similar to this caused by corroded ground points in the electrical system. To troubleshoot it you really need to have the official MB Electrical Troubleshooting Manual. Research the right headlight & wiper systems - see if they share a common ground.

On my 124 chassis car, each headlight is grounded to the chassis immediately below the headlight assembly. Look for a bunch of brown wires coming together and bolted to the frame of the car. Your 201 may be similar, seeing as these cars are cousins design-wise.