I have a '95 C220 with a few weird electrical problems and I finally realized that they are all related to the driver's door. With the driver's door open, the dome light doesn't go on, the key buzzer doesn't buzz when the key is in the ignition, and driver's seat adjustments don't adjust.
Without the key in the ignition, the driver's seat adjustment will work with the driver's door open but ONLY IF the passenger's door is also open. The seat adjustment works with the key on; that's not the problem.
All of these things used to work but gradually went bad (is the "gradually" a clue?). First I replaced both door switches, but that didn't do it (I really thought it would).
Also, just for kicks, I replaced a couple of cheap relays ($30 total). I didn't expect that to do it, and it didn't.
Any help would be welcome. :surrender: