If you hear a clicking noise, the horn relay is probably working. Find the horn (or horns) as Elizabeth directed. Pull the wireing connector off. Attach a test light or voltmeter and see if you have voltage when someone pushes on the horn pad. If you have voltage at the connector, you have a bad horn. Replace it. You may want to install a second one at the same time if you only have one. Two sound better and usually only one fails at a time so you would still have something if one fails.
The main culpret in destroying horns is water. If water gets into the horns it often destroys them. Sometimes they start working again when they dry out. If you repeatedly have a problem with flooded horns, you may want to try to mount them in a more protected area.
If you don't have power at the horn, you will need to trace the wiring back to find out where it is lost. A wiring diagram would be helpful.
