Wilsons Sandbox

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Proper electrical hookup for loud, heavy duty electric horns is important for maximum effectiveness and safety. The stock wiring harness is inadequate to handle the electrical demands of accessories that draw large amounts of current. A horn/head light relay is a heavy duty switch that handles large electrical loads safely and provides maximum current to reach the accessory. The relay is an electro-magnetic switch that allows a light duty switch (like a horn button) to control much more current. When the switch is pressed, an electro-magnet closes the circuit allowing a second circuit to pass larger amounts of current to the accessory. Stranded 14 gauge electric wire is used to connect the relay to the 12 volt power source and to conduct the current to the accessories. Thinner 16 or 18 gauge wire can be used the handle the lesser amount of current that is used to turn the relay on or off. Disconnect the wire that goes from the horn button to the stock horn & run a new wire from the disconnected wire end (at the horn) to the trigger-circuit terminal of the relay. The 2nd trigger terminal on the relay is connected to a 12 volt power source using 16 or 18 gauge wire. Pressing the horn button will result in an audible click from the relay, indicating that the relay is wired properly. The heavier 14 gauge wire is connected from a 12 volt source to one of the remaining relay terminals. The last terminal is connected to the horn(s). The final hookup is to use 14 gauge wire to connect the 2nd horn terminal to a chassis ground, using an eye hook electrical connector. The attached wiring diagram is a generalized setup for horn relays. Auto parts stores sell all the parts you will need to complete the setup. A similar setup can be used to control the high & low beams using the stock headlight switch. A DPDT (double pole, double throw) relay or two 'regular' relays would be required for the headlight setup. This setup would allow more current to reach the headlight, resulting in more light output. This is important for those running more powerful (higher wattage) headlight bulbs Additional installation tips: Buy a relay that has the relay's wiring diagram embossed on the relay's housing. Make sure that all wires connected to the relay can't accidentally short out against the frame. On my KLR, I mounted the relay to one of the 6 mm bolts that attaches to the fairing's flat plastic (rear) headlight cover. This minimizes the length of the wires and keeps the relay relatively protected. Mount the horn so that water can't be trapped inside the horn. Tilt the horns downward so that the opening points about 10 feet in front of your bike. This will maximize sound reflection in front of you and allow water to drain out. Use 3/4" X 1/8" steel flat stock for the horn mounting brackets. Aluminum flat stock should be avoided because it will fatigue and eventually break. To use the 'polite' stock horn, run a new wire from the disconnected (stock) horn terminal to a new momentary-on pushbutton switch. The second terminal on this new switch will be need to be grounded. Professor A9 Federal Way, Wa. [USA]