Wiring a horn the right way, whether to replace a non-working horn, or to install a new one to a custom vehicle is a job that a competent do-it-your self type should be able to complete in an hour or two.
Disconnect the negative terminal from the battery.
Using the self-tapping screw, mount the 20-amp circuit breaker in a protected location near the vehicle battery.
Connect one terminal on the circuit breaker to the positive terminal of the battery, using a piece of wire and two solderless ring terminals.
Connect the other terminal of the circuit breaker to Pin 87 of the Signal Stat 192 relay. Use a length of 14-gauge primary wire with a ring terminal on the circuit breaker end and an insulated solderless spade terminal of the relay end.
Connect Pin 87a and Pin 86 with a short piece of 14-gauge wire, having a female solderless spade connector on each end.
Mount the horn. Use a large self-tapping screw, and mount to an area behind the bumper or grille.
Connect Relay Pin 85 with the terminal on the horn, using a length of 14-gauge wire with solderless female spade connectors on both ends.
Mount the momentary contact switch within easy reach of the driver.
Connect Relay Pin 30 with a terminal on the momentary contact switch. Use 14-gauge primary wire.
Connect the other terminal of the switch to a metal part of the vehicle.
Reconnect the battery's negative terminal.
If your replacement horn has two terminals, the other terminal is to be connected to a metal part of the car or the negative terminal of the battery.