How To Fix Your Airbag Warning Light on 2004-2008 Ford F-150 With Sensor Repair kit
After a few years the sensor and the wiring pigtail that connects to it become corroded. Once the corrosion reaches a certain level, contact is no longer established between the pigtail and the sensor causing your airbag light to come on.
The good news is the fix is very easy in the parts needed are not very expensive.