Rear view mirror light not working properly ?

Hi I bought my Beetle in December second hand 2004 plate the rear view mirror light does not turn on properly, at first it did not turn at all when I unlocked my car or opened my doors and now all of a sudden since I've changed the stereo to an aftermarket one it turns on when I unlock the car and open the door. This is good however what is not good is when I'm driving it also decides to turn on and not only that I recently realised that the switch in the middle of the light that determines the setting was broken and stuck back on with glue!. I've told the garage where I bought my care from about this because whether they glued the switch back on or not this is not good practice, however they haven't got back to me yet about getting the new mirror light. Does anyone have a similar issue or know the solution? I have no clue what is going on just hope it's not something major.