Where is the Seatbelt sensor?

[SVX JAZZ]

Driver’s side seatbelt finally stopped working. After looking through the posts this seems like a frequent problem. Mine had some glitches a while back but I thought I fixed it. Now it:
•Stays in the up position
•Seatbelt light blinks constantly
•I manually cranked it back but as soon as I open the door it
goes back into the up position.

I seems like the sensor that tells it that the door is closed is not making a connection. Where is this sensor? Is it in the door at the latch or is it in the rear panel near the motor for the belt system?

Thanks for the help.