If its the bulb in the PAD, here's how to fix it: (from an earlier post of mine)

I had an airbag fault 2-7, which means that the little light that indicates that the passenger airbag is off wasn't working. I did a search and found that the only way Ford helps you with this is to sell you a new passenger airbag disable module for several hundred dollars. I didn't like that answer, so I decided to see if I could replace the light. Turns out you can, and its not too hard:

0. Disconnect the negative battery cable and wait at least 1 minute.
1. Remove the ashtray.
2. Pop off the cover over the passenger airbag light. It just snaps on with a couple of prongs.
3. Remove the 4 screws that hold in the ashtray track. The assembly has 2 tabs that align it - they may hold it in place somewhat, so gently pry it away from the dash. This will bring the passenger airbag disable (PAD) box with it.
4. Disconnect the electrical connector to the PAD.
5. Remove 2 screws from the bottom of the PAD, and remove it from the ashtray track.
6. Gently pry the cover off the PAD. Inside, you will find a circuit card that is connected to the electrical connector. This circuit card has a little light soldered to it. Lift it out of the PAD for access.
7. I bought a new light at Radio Shack, their number 272-334, which is a 12VDC, 65mA green light with solder leads. Unsolder the old, dead light and solder in the new light. (Test it to make sure it works before you reassemble.)
8. Assembly is the reverse of the above.

The system now works fine, and the only difference from stock is that the light I found is green instead of yellow. (Its possible that at a larger Radio Shack store they would have a yellow one, but the store I was at only had this one.)

I think if it fails again, I'll probably just solder in a resister, because I don't really care about the light, and the system just needs to detect current flowing in that circuit for it to pass the startup diagnostic.