[rotorwrench]

With a relay in the circuit, the horn body has to be grounded in order to complete the ground path of the horn coil to the horn body internally. This only requires the one wire for power from the relay to the horns. If there is no relay then there would have to be a switch in either the power side of the circuit or the ground path side of the circuit. If it is ground path the there would have to be two wires going to each horn and the horn bodies would be insulated from both the power and ground paths of the horn coils. If the switch is in the power circuit side of the horn coils then only one wire would be necessary since the horn bodies could provide the ground path. I would have to look at the electrical diagram to tell which way it was supposed to be. I know my model A has a 2 wire system