Car Components Accessories 

How to align headlights at home

Chalk a vertical line on the wall or the garage doors, opposite the centre of the car bonnet. Draw two outer lines equidistant from the centre line and the same distance apart as the headlamp centres. Drive the car close to the wall, facing it at right-angles. Bounce the car to settle the suspension, then chalk a vertical line on the wall opposite the centre of the car. Measure the distance between the headlamp centres, halve this figure and draw two more vertical lines at the same distance on each…

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Car Components Accessories 

Checking headlamps and lights

A tungsten headlamp is similar to a smaller lamp, but may use up to 45 watts. On many modern cars the headlamp bulb can be reached from inside the bonnet; on others it is necessary to remove the lamp bezel or grille on the front of the car. Failure of a single headlamp is usually confined to either the main beam or the dipped beam. In a lamp unit fitted with a bulb, this is easy to check: remove the bulb, hold it up to the light and see if…

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Car Components Accessories 

Checking and replacing fuses

Make sure you know where the fuse box is fitted in your car. The location is usually given in the car handbook. Often, the box is half hidden under the dashboard or in the front knee-well. 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. The fuses are usually grouped in a box or on a panel with a…

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Car Components Accessories 

How to test electrical circuits

A circuit tester is a useful and inexpensive tool for making electrical tests. Checking a simple circuit is straightforward – the lighting circuits are among the simpler ones – but the electrical wiring in a car contains many interlinking and branching circuits, which bring complications. All car wiring is colour-coded; unfortunately there are no national or international standards for colours. Colour codes for individual cars can be found in wiring diagrams, in the car handbook or in a service manual. Symbols are used to represent electrical components in wiring diagrams,…

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Car Components Accessories 

How to check a relay switch

Checking relay connections with a circuit tester. 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. If the component still does not work, it is faulty; if it works, then the supply is faulty and the fault will be in the relay or the connections to it. Trace the supply wire back to find the relay — this is a small metal or plastic…

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Car Components Accessories 

Checking the instruments

On many modern cars all the instruments and warning lights are on a display panel that lifts out in one piece. 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. Clocks, radios and other accessories are usually beyond the scope of home repair, but you can check their connections and remove…

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Car Components Accessories 

Car horn not working?

The horn may be operated by a stalk on the steering column or button in the centre of the steering wheel. If the horn fails, check whether the fuse is sound (See Checking and replacing fuses). If it has blown, fit a replacement and check the horn again. If the fuse is sound, or if a replacement fuse blows, there is a fault in the circuit or the horn itself. Because they are low down at the front of the car, horns often get wet and dirty, and the connections…

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Car Components Accessories 

How a speedometer works

A flexible drive cable inside a flexible tube links a small magnet inside the speedometer to the gearbox output shaft. The magnet rotates with the shaft and its magnetic field attracts a metal drum to turn the speedometer needle against the force of a hair spring. The needle moves round the dial until the restraining force of the hair spring brings it to rest to give a reading of the road speed. Of all the instruments you can find on a modern car dashboard, only one is a legal requirement…

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Car Components Accessories 

Working on the wiring system

Use a circuit tester to check if single wires are damaged. The wiring loom itself seldom goes wrong, but after other repairs have been made, a cable may be trapped and its insulation cut through, causing a short circuit. If this does not blow a fuse the wiring overheats and melts insulation, perhaps starting a fire. A similar result can come from fitting accessories incorrectly, or if power demand is too high for the size of the wire being used. After many years, insulation may become hard and brittle, particularly…

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Car Components Accessories 

Fitting a new speedometer cable

The speedometer cable is driven from the gearbox, and curves smoothly up through the engine compartment and the bulkhead to connect with the back of the speedometer. 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. If the gauge needle does not move at all, the inner cable or drive may be broken; or the cable’s square ends may have become rounded with wear and fail to engage in the sockets. The fixings at…

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