My tech called me today with an interesting problem: one of his customers had a broken right side (passenger) outside mirror.
Simple enough! He ordered a replacment and it didn't work! So they gave him another one: same story! So he notified his part man at Mercedes of San Diego who, in turn, went back to New Jeresy for techical help. No soap!
So here's what I found. The new units are wired 'wrong' if you use the older mirror as a guide. It's from an '83 300SD.
When the NEW part is installed the mirror will only move in just one direction.
As you can see, the motor wiring is identical on both, so the connector wiring should be also!
To fix the wiring (without re-wiring the car), do the following:
1) Remove wires in pins 1, 3, and 4 by releasing the holding pins.
2) Move the green wire to pin 4
3) Move the white wire to pin 1
4) Move the black wire to pin 3
That fixes it! Of course, you need to take the mirror assy apart but that's easy. Remove the mirror by releasing the spring: then loosen the screws to remove the back aluminum assy. Peel back the protective covering over the pins.
Hope that this helps some W126 owners.