un known light and switch

[Niall]

The light will come on every time you start the car. If it goes out shortly after, ignore it, as it means the airbag is functioning properly. If it's on all the time then it is switched off as welshpug says.

Wrong. The left and middle one (if it has side air bags) will come on but the right hand one won't. Like welshpug says, its only comes on when someone turns the passenger air bag off with the key switch.