There's one in the trunk on the driver-side of the car, but before you go on a wild goose chase....the seat belt light and airbag light I think have something to do with each other but nothing to do with your radio.
You should check under your seats and make sure there isn't 50 water bottles or a collection of tim hortons cups that pulled the connector apart when the seat moved. Double check the connections going from the wires coming out of the floor to the bottom of your seats.
If nothing was unplugged and the wires don't look like they lost a battle to tug-of-war, I suggest you have your electrical scanned. It will probably say your seat belt tensioner is pooched. Also something about your radio...
If airbag, seatbelt light came on the same time the radio stopped working then its probably something in the dash.
If the airbag, seatbelt light came on before the radio acted up or afterwards, its probably not related.
Then you can pull all the the carpet out of the trunk and remove the panel on the driverside (in the trunk) if you have a cd changer then you should be able to see it, if not I think there will be a little black box or something....anyways there's a ground point around there....but again to avoid taking all the stuff out of your trunk....get the car scanned.