I have not wired mine yet but plan to do so. The way I understand it- you have a hot wire from the amp gauge (or other hot source) to one post on the relay. The horn button completes a circuit to ground. The wire from the horn button goes to a post on the relay that grounds the relay and allows to power to travel from the hot lead through the relay and out the 3rd post which goes to one lead on the horn. The second horn lead needs to be grounded.
The advantage of wiring it this way is the horn button and the tiny spring within only has to act as a ground to make the relay pass current to the horn. Without a relay a much larger current flow must go thru the horn button apparatus and the tiny spring often gives up the ghost.
Chuck
