Most likely it's the relay when they click. If there were no clicking and you had power at the horn when the button was pressed, you'd need to take a screwdriver handle and give the horns a whack to free up the diaphram inside. BUT, if you are not getting power to the horn, and if it's NOT the wiring leading to the relay, then the relay is toast. Use a tester to see if there is power going into the leads on the relay while someone holds to button down. If there is power going in, and nothing coming out, toast.