Hi, Had the very same problem on my 200SE, Found it to be the drivers door pin switch, This is situated just below the door catch on the drivers side pillar, Undo the philips head screw, Remove the switch with the cable attached, Remove the cable from the switch use a bit of masking tape to stop the cable dropping down the hole.. them clean the contact area of the switch where the screw goes through andwhere the wire fits on with a fibre pen or fine sand paper, Reaasemble and test, Mine was a bit tarnished and wasn't grounding out every time the door opened, so the interior light wouldnt come on, the auto lights would stay on and the buzzer didnt beep. took ten minutes to do, no further problems.. :D