DIY: Air Horn Wiring

Air horns get through to distracted drivers.

Air horns are an annoyance when used improperly, but they can be lifesavers under certain circumstances. The huge sound they produce definitely attracts attention, making them a popular aftermarket item with motorcyclists and small car owners. Once all of the components are installed on the vehicle, air horn wiring is usually accomplished by hooking it up as an adjunct to the existing horn.

Things You'll Need

• 12-volt horn relay
• Power drill and bits
• Self-tapping screws
• Screwdriver
• Wire cutter/stripper/crimping tool
• 12-gauge automotive wire in both red and black
• Crimp-on terminal connectors
• 30-amp inline fuse holder
• 12-volt test light or multimeter
• Tap splice connector
• 30-amp fuse

Instructions

1. Decide on a location for the horn relay, preferably in an accessible spot near the air horn compressor or existing vehicle horn. Mount the relay to the vehicle body or frame. Drill a hole and use a self-tapping screw if necessary.

2. Attach one lead of a 30-amp inline fuse holder to the positive battery terminal. Connect the other fuse lead to an appropriate length of red 12-gauge automotive wire. Run the wire neatly to the horn relay and connect it to relay terminal 30. Attach another length of red wire between the positive terminal of the air horn and relay terminal 87. Position the wire neatly out of the way.

3. Examine the existing vehicle horn to determine the positive and negative wires. Test the wires if necessary by disconnecting each one in turn and connecting it to a multimeter or 12-volt test light while pressing the horn button. The positive wire will either read 12 volts or cause the test light to glow. Reconnect both wires to the existing horn.

4. Slip a tap splice connector over the positive horn wire. Attach a length of red wire to relay terminal 86. Insert the other end of the red wire into the opposite side of the tap splice connector and crimp to make the connection.

5. Run a short length of black 12-gauge automotive wire from horn relay terminal 85 to a suitable ground. Run a short length of black wire from the air horn negative terminal to a suitable ground. Drill holes and attach the wires with self-tapping screws if necessary.

6. Insert a 30-amp fuse into the inline fuse holder. Press the horn button to check operation of the air horn.

Tips & Warnings

• Check your local noise ordinances before installing an air horn. Some jurisdictions frown on their use, especially in residential areas. Wiring a cut-off switch to the air horn to prevent its use in town could help you avoid a ticket.

• Consult the wiring diagram that came with the air horn and/or horn relay if possible to confirm the correct terminal connections.

• For a neater finished appearance, run the new wires alongside existing wiring where possible and secure them with zip ties.

• Have a supply of spare fuses on hand in case you accidentally cause a short circuit.

References

• PBase - iamflagman: Wiring Diagram for Air Horns Using Stock Grounded Horn Button
• Gadget's Fixit Page: Air Horn Installation