the fuse... and/or the multiplexer.

someone before had to replace the entire driver's side multiplexer unit since he shorted out the dimmer wire

 

just don't hook up the illumination wire, i've always found out that causes more problems than good. i once hooked it up on a jeep chereokee and it killed the whole dash until i unplugged it. for your seatbelt i've never heard of the radio doing anything to it. i know the srs should be wired independantly from the rest of the car as a failsafe. i would check the door pins and see if they're corroided and not closing the circuit. also i know honda has a lifetime warranty on their seatbelt systems. also was there any work done in the kick panel and door speaker areas?

 

Oh ya, your right. I totally forgot about that...he had an accord also, right?