I would imagine it's the one on the nearside that operates the light. My light hasn't worked since I bought the Bongo, but I suspect that's a blown bulb.
Some while ago I raised the roof to check it out, and when I lowered it again the beeper wouldn't stop. That turned out to be the offside microswitch. As a "temporary" repair (to shut it up!) I disconnected the wires to the microswitch and joined them together with an insulated joint. I really will get round to replacing the microswitch one day, honest.
Now the bad news.

The nearside microswitch is much harder to get at as the wiring is completely hidden. I couldn't see how to get at that one without removing the roof!
