1st, check the fuse box, read on the label and then test for a current. if has a current and the fuse is good, go to step 2
2nd, check under your seat where the electric seat belt motor is, test it to see if there is a current. If not re-trace steps.
Last but not least if all else fails and you have failed as a handy ameture mechanic, take it to a nissan dealership n the seat belts have a warranty i hear, once again hearsay. It doesnt hurt to call and ASK. My personal advice do it your self so you dont have to rely on other ppl and it cheap. lol
I have a 19990 240 SX.
The seatbelts have a lifetime warrenty. I called my local dealer and was told it was out of warrenty and any collision or electrical modification voided the warrenty. So I called Nissan North America who said the dealer should never have told me that. They contacted the dealer. Both sides, motors and tracks were happily fixed that week although they did not replace the frayed belt.