As you probably know a plug goes to each seat belt pretensioner. If one is disconnected (i.e to change a double seat to a single) the air bag light will illuminate. With the right equipment and knowledge you can re programme the computer to stop this. Or you can just connect something else in place of the missing pretensioner to fool the computer into thinking its still connected - a sidelight bulb or 2.2 ohm resistor should do it (try ebay or Maplinsl