The horn switch is located on the hub of the steering wheel.
The pre-'92 horn relay is under the dash, near the cruise control servo above the gas pedal, and it's an old Ford-style relay. You probably got a Bosch-style relay, right? Look at these pics:
But russo's right - if it's clicking, it's probably fine. I bet those "new" horns are bad, or their wiring has come loose. If you paid the shop to install them, take it back & complain.