When the Air Bag light is on, this means there is a problem in the restraint system. Unfortuantely, there are literally dozens of parts/sensors monitored in this system- from a faulty seat belt, to a faulty airbag sensor. It is a fairly "big" issue, seeing as if you are in an accident, the air bags will not deploy which could result in serious injury. Your best bet at this point is going to be to have the "codes" read from the on-board computer. You will need to find a shop that has a scan-tool that can read airbag codes, as most local "free" scans or "personal" scanners do not read airbag codes. Once you have these codes you can more accurately and efficiently begin the diagnostic process and then make a repair.