Horns with relays work like shown below.

As far as wire colors and which terminal on the horn and relay is which, that depends on the relay and wiring harness makers.

Once connected properly you should be able to ground the "switch" terminal and the horn should honk.

When properly connected you should have zero volts on the wire to the horn, battery volts to the other 2 wires.

When pressing the horn button you should have zero volts to the horn button and battery volts to the other 2 wires.
Attachments
horn relay.jpg (36.45 KB, 49 downloads)

Last edited by Bill Hanlon; 09/13/2026 5:40 PM.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.