This one may be better left to a shop, as to test it properly, you need an air bag simulator.
Troubleshooting the issue can be a little complicated, as it involves measuring resistances in the circuit, which require you to have an airbag simulator. Basically, if you have an airbag simulator attached to the system instead of the airbag, and the light doesn't flash a code, you have a faulty airbag, which you could get from a junkyard (keep in mind some states require you to document certain information, like the vin of the car the airbag came from. If you still get the code, the next step would be to measure resistances from the diagnostic monitor connector. If those resistances check out, you likely have a defective diagnostic monitor (blue box). Those should still be available new from Ford. There's always the chance you have failures in more than one of those systems (diagnostic monitor, wiring, and airbag).
It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt.