The rear driver's side door window in my '91 190E 2.6 won't operate. I opened up the door and saw the tension wire that raises/lowers the window was broken. I removed the entire assembly and replaced it with one that was working on another 190E I own. After installation, it still won't move. All the other windows work and the plugs/wires/switches look okay to me. I've replaced the switches with ones I know work, but still nothing. What steps would you take to track down the problem?

THANKS!