Is the switch defective, or is it just disconnected?

I just did this to re-connect the mirror switch on the '97 S320 I just bought.

You can see the connector by carefully prying up the plastic surrounding the
shifter area. To actually get the switch out you would need to remove the
wood console. I only took mine apart enough to push the connector back into place. All the switches press downward for removal.

If you are not mechanically inclined, I would recommend taking it to a MB independent shop rather than the dealer.

Here's what I did.

1) Remove the ashtray insert. Slide the plastic lock to the right.
2) Remove the small screw that attaches the front wood to the ashtray.
3) Now there should be some very tricky screws facing backwards toward
the rear.
4) Carefully pry up the plastic piece that surrounds the shifter area.
5) Remove the radio. You need the special radio tools that go in the slots on the front of the radio. They are cheap.
6) The wood piece attaches to a plastic clip at the rear of the console.
7) There is a special tool to release this clip. Mine had been broken by the
dealer tech (term used loosely) who was in there previously. They just left it broken.

I didn't have to remove the console wood. So that's all I know.

Steve