Alert signal problems

I have a '99 VW Golf, just today having problems with several of the electronic characteristics: central locking not working, left rear door not responding to central 'lock' function when key is used in drivers door; alarm does not set with key in drivers door is used to lock car; interior dome light does not go off when drivers door is closed (seems as if car thinks door is open); when driver's door is closed and engine is running, signal alert 'dings' constrantly, when turn head lights on signal alert tones constantly.

I was thinking that possibly the electric switch ($170.00) in the driver's door behind the keyway is the source of the problems, I seem to remember I had another car that similar issues and switch in door behind keyway was replaced and problems were resolved.

Thoughts welcome, thank you.