Don't assume your relay is bad from a click. Mine is 43 years old and clicks--and the Moss replacement doesn't work at all.
The click is normal, and can be the result of insufficient voltage reaching the relay. Does it click when the car is running at 2000 RPM--or does the horn work at higher RPMs?
Another likely source of issues are the wires and grounds that go to each horn. Carefully clean those. They were my problem.
Of course, no horn on a 4A will work if the horn button in the steering wheel isn't grounded. Be sure to check the ground straps on the steering column. Those are easy to overlook and are the problem a good percentage of the time.
Good luck.