A fix for wiring issues
 

I had the same problem with my 79 300td ,the switches for the windows had been not working and found a quick remedy ,remove the plastic backing that holds the wires in place in the holder ,then make a quick diagram of the wires,then with a needle nose plyer ,just lightly tighten the gap in the female wire .I did the same procedure on my 300cd today but it was the turn signal relay switch ,tighten all the female ends up ,just a touch and it worked like a charm ,put back the wires and cover and I was in business.

By the way the relay for your turn signal lays under your consul near the shifter on a 85 300cd ,I was looking under the dash all this time.