Fault finding.
Is power getting to the horn when the button is pressed?
Check with multi meter.
If yes, it is probably the horn at fault. Replace or strip and fault find on the bench.
If no, check the horn push button contacts and recheck all the connection including replace the fuse.
You could also connect a battery across the horn terminals to isolate the horn from a wiring problem.
Just work through it methodically and you will find the problem.
New horns are not very expensive.
