Another success story from having this excellent technical website.

I had a problem with my '82 240D which had to do with the seatbelt light coming on every time I would press the brake, use turn signal, use windshield wiper, or anything else that required me to activate a switch....it was very annoying. I did a search, and wouldn't you know, another person had posted the same problem I was having.

The solution: replace the voltage regulator. It was very easy to do for the DIY. Now no more intermittent seatbelt light or buzzer! Problem solved!