The problem is not the window regulator. All that is fine.

My mechanic took out the comfort module, the thing underneath the rear seat, and if he plays with that, he can get the window to go up or down. I think he said somehow just that one window is not getting ground.

He couldn't fix it so I said I'd get a replacement part which I just got today. I put it in, and same problem. Left rear window won't go down.

Any suggestions?

1991 300d, 252k