I just (yesterday) bought a very clean '94 325 Convertable. On the test drive, and on a subsequent drive with a passenger in the seat, the airbag light was off and life was good.
Then, I had my first back seat passenger and a front seat passenger at the same time (my kids had to go for a ride - before that it was just me and the front seat passenger). Anyway, my daughter moved the seat forward so her sister could have foot room in the back seat, and the Airbag light came on. A cursory inspection of the underside of the passenger seat showed that all was good, but a more detailed inspection may show otherwise. I have never had trouble with the Airbag light before, except that on my old car (another '94 325i) the light came on to tell me the light didn't work.
What can make the Airbag light come on when the only obvious activity has been the moving of the seat?