The horn is an electromechanical apparatus fitted in the car which produces a loud noise, intended for use as a warning signal. The horn would be applied in an emergency situation, with the intention of avoiding a possible accident or a dangerous situation. The horn should only be used as an alert to other road users, to inform them of your presence.
The horn is usually housed in a metal casing, which acts as an amplifier, and situated under the bonnet in the engine compartment, behind the front grille. It's normally secured in a bracket which is bolted into place. The horn should be fully functional with all components fitted securely and in good working order. The design of the front grille is usually such that the sound emitted from the horn can travel and dissipate through it and out of the car, enabling it to easily be heard by other road users. The controls to operate the horn should be within easy reach of the driver and working properly. The horn is usually operated by a control on the steering column stalk or by pressing a button in the middle of the steering wheel. There are many different horns on the market with a variety of sounds. To ensure a product that complies with MOT regulations and one that will be a simple to fit and suitable for your car, it's worth buying the horn which is designed to be compatible with the make and model of your vehicle.
There are typically two types of horn used in passenger motor vehicles but both work using a diaphragm, normally constructed of spring steel, which vibrates to produce the sound. A higher frequency/HF horn has a diaphragm with a resonator plate fixed to it which serves to amplify the sound. A windtone horn uses a trumpet design which amplifies the sound when the diaphragm causes air to vibrate through it. Both types use electromagnetism, with the use of a coil wire which makes an electromagnet, to make the diaphragm vibrate which produces the sound. Essentially, the horn has an electrical contact which is attached to and activated by the diaphragm, and works with an electrical current sourced from the car's battery.
Because of their location in the vehicle, horns are subject to damage from water and dirt which can cause the electrical connections and mounting bracket to corrode. Rust is a common cause of a malfunctioning horn. Faults can arise with the circuit, cables and connections, the horn itself or the operating switch. It's important that a broken horn on a vehicle is replaced as soon as possible. Buying the horn will guarantee you get a part that's manufactured for your specific car make and model, giving you the ideal replacement that will fit well and perform properly.