Take your volt meter and see if you have power coming out of your relay, where the horn hooks up...If so, look at the wiring to the horns...run a jumper wire to the horn from the relay and see if it works.
If not, then it might be the relay. They are simple, if I remember right, and if its clicking then the electric magnet inside is working OK..the contacts can be cleaned with fine sandpaper, then use a contact grease to get a good contact.
Look at the easy stuff first...wiring.
I hope I've help...