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Your Horn worn out? » Read more about common malfunctions • Repair • Replacement manual
Noisy on purpose: the horn
The car horn is a manually operated warning signal for other traffic participants. Its impeccable functioning is relevant for passing MOT. Yet, it should only be used when necessary.
Horn: construction and position
The horn is an electromechanical component. Its construction is as robust as it is simple. This keeps its purchase price low and at the same time ensures a long life span. The horn is fixed to the bodywork with an iron bridge and connected to the onboard circuitry by two contacts. The horn is not grounded via the bodywork. The connection is generally made by way of a pre-fabricated double plug. The car horn is usually located behind the front bumper or alternatively fixed to the radiator grille. The generated noise must be directed conically forward. Changing its direction compromises its effect. The horn has a flexible electrical contact, attached to - or actuated by - a thin metal diaphram. A strong electromagnet, setting a central armature in motion, is connected to the diaphragm. When current is applied to the electromagnet, the armature moves to its mechanical limit, momentarily disconnecting the current supply. As it relaxes back to its starting point, it makes electrical contact again. The procedure is repeated several hundred times per minute, generating the typical sound of a horn.
A horn can fail because of penetrating moisture. When the internal components, like the contact breaker points or copper coils corrode, the horn soon is beyond repair. This is noticed by the fact that it no longer functions at all. If it still produces a croak, repair can be attempted: the horn is equipped with a screw for adjusting the contact breaker point. By turning this screw, the function can be restored.
Car horn repair
If the inner core of a car horn is fully corroded or burnt out as a result of a short circuit, it usually cannot be repaired. The only option is replacement. This is very easy: the horn is fixed to a thin metal bridge by a screw. It can be accessed by removing the bumper or the radiator grille. Now, the horn can be easily removed. Prior to installation, contact points should be checked for corrosion. The plugs are somewhat difficult to clean. If this does not work, the plugs must be renewed as well.
The horn: legally
Replacing a car horn implies installation of an original spare part or at least a approved component. This specifically applies to multitone clarions. It is possible to upgrade the horn by tuning. Nevertheless, only authorised systems with a verification code should be used. "Duke of Hazzard" dixie horns are illegal on the British Isles and the Continent. Their use can incur a fine. The installation of multitone signals is severely prohibited. Imitating a police siren is a serious offence which can lead to proceedings on charges of assumption of authority.
Buying a car horn
Car horns are very cheap, starting at 5 EUR (± £4,50). The accessory trade offers a wide range of special horns, suitable for modification of the horn sound. Nevertheless, the authorisation of the product should always be checked. Operating a horn requiring an air compressor is generally reserved for large vehicles. Trucks and buses are traditionally equipped with these horn types as they need to drown out the noise of a large diesel engine. Their use in family cars requires approval.