The reason you have no answers is because you've been told the answer several times in various other threads. Get the FSM, get the wiring diagram, and troubleshoot. Nobody can snap their fingers and give you a magic answer, the only way you're going to find the issue is to start at the source, take a multimeter and start tracing the circuit. If that isn't something you can do yourself, find an automotive electrician and have him trace the circuits to find the fault.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)