The car will have two horns,one low tone and one high tone.
These are if I am correct wired up constant live and the the horn push button sends the earth to complete the circuit.
Take the wires from both and then replace the fuse.
Connect one horn up and see if fuse blows,if not then the other.
If fuse blows with them disconnected then look at wiring for chafing where it runs under bodywork