I'll check today.Check the fuse for the horn. On my 1980, it's the 3rd from the bottom on the ride side. It's a 20A.
There is a horn relay in the engine bay, just near the battery box on the passenger side. It's just forward of the EFI relay. You can see what I'm referring to in the factory service manual, Electrical System, page EL 100. EL 34 shows the wiring diagram of the blades on the relay (12V, ground ,etc).