Question: I have been told the reason why the overhead dome light doesn't come on when I open the driver's door (All other doors open turn on a light) is due to a failed seatbelt relay, a $60 part. My puddle light on the drivers door won't come on, either, unless the pass door is open. However, if the lights are on and I open the pass door, the buzzer sounds. If I have the key in and open the pass door, the buzzer sounds. If I open the pass door the dome light comes on and the red seatbelt warning light comes on. Is it really the problem, or is it something else?

Thanks

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2002 Mercedes-Benz E320 4Matic
1995 Mercedes-Benz E320 Wagon
2005 Land Rover LR3 V8 SE
1999 Audi A8 4.2L quattro