The wiring diagram we provide for the harness does not show a horn relay. The key listing states it's # 14, however no 14 illustration exists in the diagram. The brown/white wire is never a switched live wire, rather it’s a switched ground, as there is no power to the handlebar switch, which simply completes the ground. The power gets to the horn relay via the solid red wire, which is powered as long as the battery is connected.

Both ground and power are required to activate the relay and ground is also required to move the relay contacts, hence the solid brown wire. The black is power out to the horns, which are grounded via their mounting to the frame.

Note that when the new handlebar switches arrived for 1979, the internal contacts were robust enough to handle the load and the horn relay disappeared. The 1978 handlebar switches were holdovers from the ‘75 /6 when no bikes had dual horns and again, a relay was not present. Dual horns required more power, too much for these switches, even if they were just creating a ground. The ‘77-‘78 bikes without dual horns, /7 & S, did not have a horn relay. 1979 was a year for lots of rationalization, same 1000cc engines and rear drives for all versions and same frame wiring for all Airheads, except the R65.