This is Clay, I'm a certified master automobile technician with 30 years of automotive repair and diagnostic experience.
From your description most commonly the drivers seat belt buckle has failed. The buckles can be checked by disconnecting the seat belt switch and jump terminal #1 to terminal #2. With the ignition switch in the on position the set belt light should come on for approximately 4 seconds and go out. If the light operates properly with the connector jumped the switch in the buckle has failed. The link below is a connector view.
Drivers Seat Belt Switch Connector
Make sure you're on the proper connector, jumping any air bag circuits could deploy an airbag. If you need the service procedure for replacing the buckle let me know.
WARNING: To avoid serious or fatal injury on vehicles equipped with airbags, disable the supplemental restraint system before attempting any steering wheel, steering column, airbag, occupant classification system, seat belt tensioner, impact sensor, or instrument panel component diagnosis or service. Disconnect and isolate the battery negative (ground) cable, then wait two minutes for the system capacitor to discharge before performing further diagnosis or service. This is the only sure way to disable the supplemental restraint system. Failure to take the proper precautions could result in accidental airbag deployment.
I hope this information is helpful. If you have any questions let me know. You can reply back to me through this thread at any time.
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