The fuse F1 is blown.

Replace the fuse F1.

The seat belt warning lamp wiring harness is open circuit or short circuit.

Repair the wiring harness.

The continuity between the 2 terminals at the switch side of the connector has failed.

Replace the seat belt switch.

The continuity between the terminal for the BLK wire and ground has failed.

Repair the open ground.

The warning lamp bulb in the instrument cluster is blown.

Replace the wiring lamp bulb.