Accessories

Speedometer failure is likely to be caused by a fault in the cable that runs from the gearbox to the back of the speedometer gauge. Read more

The oil pressure gauge is one of the most important instruments in a car. It acts as an indicator of the engine 's overall well-being and as an early-warning system, giving advance notice of any problems so you can investigate the cause before an expensive breakdown occurs. Read more

The electrical wiring in a car is a system of colour-coded wires called the loom. Where several wires run side by side they are bound together with insulating tape or plastic sleeving. Read more

If there is trouble without an obvious cause in any electrical component, test the circuit to find the cause. Read more

When an electrical component stops working the fault may be in the component, in the electrical circuit or in the fuse that protects them. Because the fuse is a likely cause, and the easiest to check, look at it first. Read more

It is an offence in law not to have all obligatory lights working. Check them frequently, especially before a night journey. Walk round the car while someone works the switches . Read more

Disconnect the battery . Remove the electrical connections from the motor , preferably labelling them so that you can refit them to the right terminals . Read more

Only a garage with special equipment can align headlamps accurately. However, you may need to do it temporarily yourself if you have had to remove the lamp unit or fit a new one. Read more

Sealed-beam headlamps are simple to change, but the way of gaining access to them varies from car to car. Read more

There are two basic types of flasher unit. One is operated by a piece of wire or a bimetallic strip which expands and contracts as it is heated by the current ; the other is a relay operated by a transistorised circuit . Read more

Cars are usually fitted with a high-frequency (HF) or windtone horn as standard equipment, normally located behind the front grille. A vibrating diaphragm makes the sound in both types. Read more

A car usually has up to six main instruments — speedometer and tachometer (rev counter); fuel , oil-pressure and water-temperature gauges; and voltmeter or ammeter (depending on whether the car has an alternator or a dynamo). There may also be a battery-condition indicator, which is a form of voltmeter. Read more

If a component that is fed with electricity through a relay (See How car electrical systems work ) terminal of the battery to the feed terminal on the component, thereby bypassing the relay and supply wiring. Read more

The windscreen-wiper mechanism needs little maintenance. At service intervals drip a little oil down the wiper spindles from outside. If they stick, the motor could burn out. Read more

Electric radiator-fan motors are switched on either by the ignition switch - and run while the engine is working - or by a thermostatic switch . Read more

Car radio interference originates usually in the ignition system, the charging circuit or among electrical accessories. There are several checks you can carry out to trace the source of the interference. Read more

The car's heating system consists essentially of a motor-driven fan to blow warm air from the engine bay to the car's interior. Read more

Of all the instruments you can find on a modern car dashboard , only one is a legal requirement - the speedometer and its built-in milometer (also called an odometer ). Read more

There are a number of possible causes for a rear window heater not working, including a blown fuse , a broken or chafed wire, a faulty switch , a damaged heater element or a bad earth connection. Read more

The majority of indicator stalks are mounted on the side of the steering column so you can easily operate them without having to release your grip on the steering wheel. Most modern stalks also have a self-cancelling device that is operated by the moving part of the steering column. This automatically switches the indicators off after you have turned into a bend. Read more

Reversing lights are not generally a legal requirement but they are useful. They serve two purposes - to warn other road-users you are about to reverse, and to provide light if you are reversing in the dark. Read more