What happens, when the horn button is pushed, it grounds itself to the wheel hub, through the switch ground stud ( that runs on the button side of steering wheel) to the rely. This ground makes the circuit in the rely complete so the coil pulls the contact down to let the voltage through to the horns. You have three connections at the rely, 12 vdc, ground and 12 vdc out. A rely is used were you do not want to have voltage going through a device that do not need it, like the turn signal switch.
Time to go to work, if you need help it will have to be tonight. PM me
Good luck
