Well, first thing I would check is the fuse box.

After that, I would try shining a bright light directly on the sensor. Still no dice, I would make sure the circuit is getting voltage.

If the circuit is getting voltage, then the sensor or the transistor that drives the electrochromic mirror may be bad. I've never worked on this model car before, but if you can get to that transistor you can check it for open/short with a DMM fairly easily.

Do you have the MB DVDs? If not I can look it up for you.


Cheers.