To revive an old thread. I got my car 3 weeks ago CPO. The seat belt warning light in the dash started randomly going off a few days ago while driving and every trip since.
Rather than brining it to the dealer, I figured I'd check the wiring harnesses first (I'm an Electrical Engineer

). Sure enough, the 2 wire harness to the seat belt was a bit loose at the connector. I squeezed it together and pushed all the wires into the connectors to make sure they are fully seated. Also, the harnesses are nicely lashed to the seat frame and the chassis end of the harness was a bit tight, so I tugged some slack into it. I had the Easy Access seat setting turned on so it was probably tugging on it each time the seat moved back. Ended up turning that off anyway since I found it more of a pain that I could barely reach the brake pedal when entering the car to turn it on, lol...and I'm 6' tall.
Knock-on-wood, the light hasn't come back yet. And if it does, I'll probably just short the chassis end of the harness together to keep it OFF
Last note: to get to the harness, I just pushed the seat all the way forward and as high up as it would go. The seat belt harness is a 2-wire, yellow colored harness on the right side closest to the seat belt receiver. There are 3 harnesses under the seat...a large one in the middle and another smaller one on the left side.