How to install an air horn
An air horn is an auxiliary horn that uses an air compressor to produce a tone that is considerably louder than a factory car horn. Usually, air horns come with a compressor, relay, tubing and two horns that each produce a different tone.
However, two-tone horns are illegal in the UK so you will have to limit yourself to a single tone version. Air horns are typically installed on lorries rather than cars.
Open the bonnet of the vehicle and find a good place to mount the horns. The horns should be mounted facing at a downwards angle to prevent water from collecting inside. They should also be located towards the front of the vehicle.
Mount the horns to the vehicle using self-tapping screws and the mounting hardware provided. Avoid mounting the horns in places where they will be subjected to excessive heat and moisture or near any moving parts.
Mount the compressor to a wing with the appropriate hardware. Run the provided tubing from the compressor to the horns. Avoid running the tubing near hot or moving components. When possible, run the tubing with factory wiring harnesses and secure it with nylon wire ties.
Use a multimeter to locate and test the horn wire. This wire will read 0 volts at rest and 12 volts when the horn is pressed. This wire can easily be found at the horn itself or at the horn relay. Connect the horn wire to the relay along with power, ground and the 12-volt output to the compressor, according to the instructions included with the air horn kit. If the instructions are not available, wire Pin 87 of the relay to 12 volts, Pin 85 to the horn wire, Pin 86 to ground and Pin 30 to the positive lead on the compressor.
Mount the compressor to the wing or somewhere free of water and excessive amounts of heat. Connect the negative terminal on the compressor to ground. Test the air horns by pressing the horn button. If installed correctly, the air horns and factory horns will sound.
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