Confusing window motor issue

[rgnprof]

My 1984 300D front passenger side window just quit in the down position. I have followed all of the TS steps as outlined in previous posts - I think!

I have pulled and swapped both window switches - neither work on the passenger side. I have pulled the door and tried to check the wires - with key ON I have 12v at both wires on the block in the door (3 screws, 2 wires - one black and one green). When I depress the switch while testing voltage at either wire - black or green - the voltage drops to 0 and stays there. Release switch to the neutral position and I again have 12v.

Removed the 2 wires leading directly to the battery and applied 12v - window goes up and down (so motor is fine).

What am I missing here?

Thanks in advance. Ryan