You have the pleasure of experiencing federal legistlation in action - the mandated seatbelt warning system.
It's job is too sound a skull piercing buzzer until you buckle up. Some units were supposed to time out but it wouldn't surprise me if the control box glitched & stayed on. I bought a '73 dart from a junkyard, & the buzzer was the only thing that worked when I dropped in a battery.My fix is to set the parking brake, turn key on, put car in gear (engine off - make sure the car doesn't roll away) & track down the buzzer & unplug it. As I recall it's a small metal box - about 3" x 2" x 1 1/2" (looks like a horn relay), mounted under dash on left kick panel with a 3 wire connector.
for the dash light, either cover it with tape or remove the bulb socket.
I think the control unit was some little plastic(?) box with wires on it - behind or below the instrument cluster.
That fuse probably powers other circuits on the car so I'd leave it in.