I had the same problem with my 1995 E420...interior light stopped coming on when door opened. I checked all fuses, then bought a new door plunger switch from the dealer, which I thought might be the problem. Didn't help. I got lucky, however, when I pulled some of the plunger switch wiring out through the hole and found where several wires had been joined together by twisting them and taping. The electrical tape had come partially off and the wires were shorting against the body. I retaped it properly and no more problem. May not be your problem though.