First, Welcome to the TDR!
I`m not too familiar with the 98+ interior, but I do know there is a seat belt switch in the drivers latch. Check at the base of the latch where it bolts to the floor, and disconnect it. You could also jump the pins on the floor side so it wont bug ya about the seat belt anymore.
If that isnt it, you may have a dirty or bad connection somewhere... Try checking the connections at the PCM on the firewall behind the airbox, and check your battery terminals for any corrosion. Hopefully it isnt a computer error or failure. .
good luck
-j