Looking for some help here. Car is 1990 W126 300SE. The problem is the driver's door switch functions do not work with the door open - only with the key on, or with the passenger door open. In other words, when I open the driver's door I get no interior lights, seat adjustment switches do not operate, and worst of all, the buzzer indicating lights on or key in ignition also does not sound. I have replaced the door switch/button, with one known to be good. I suspect a relay, but don't know which direction to head next. Everything on passenger side door works fine, in fact all functions on drivers door with passenger door open.

I hope someone can help point me in the right direction.

Thanks, Jon