the serach feature is your friend, There have been dozens of horn doesn't work threads lately.
Things to check right off.
Jumper 12v directly to the horn from the battery. Make sure that the horn actually works before you go tearing into wires. The relay clicking is a good thing.
Check all the grounds for the horn. Pull it off the mount, clean up the bare metal, put it back together with some Ox-guard.
Use a voltmeter and attache it to the horns positive wire, have someone lean into the button and see if you get 12V.
Let us know the results.