airbag light

Recently the air bag light has lit. I have not been in an accident. I was working on the ignition lock and removed the cover under the steering columnand noticed the light just a little bit later. The car is a 2000 Focus ZX3, with 175000 miles. I'm a little hesitant to take it to the dealer I did remove the tumblers from the lock to free up a stuck lock cylinder and that worked well, no need for a new lock. Any help would be much appreciated. Mike