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Working on the wiring system

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

How to test electrical circuits

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

Repairing an electric window

Electric windows are being fitted to more and more cars as standard equipment, while conversion kits are available to suit most models. Read more

How to check a relay switch

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

Checking the batteries

Most car batteries are sealed for life - apart from a small vent hole which allows gas to escape. They never need topping up. Read more

Using a car battery charger

Frequent short trips, with constant stopping and starting, make your battery work very hard, especially in winter when heater, headlights, heated windows and wipers may be working most of the time. Read more

How to test a car battery

When carrying out any tests on the engine while it is running or turning over, keep hair and loose clothing away from belts and pulleys. Read more

Testing an alternator and checking output

Check drive-belt tension by pushing or pulling the belt inwards at the centre of its longest straight run. Measure the deviation with a ruler. Read more

Checking and replacing fuses

The type and construction of fuses varies from car to car. Read more

Checking headlamps and lights

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

Checking the electrics with a multimeter

Modern cars have a large amount of electrical equipment which can go wrong and so need checking. Read more

Checking a starter circuit

If the starter does not turn the engine although the car battery is in good condition, the fault may be a simple mechanical one or it may be an electrical one in the starter-motor circuit. Read more

Overhauling a light cluster

Many modern cars are now designed so that their lights are built as a one-piece unit known as a cluster. These are easier for the manufacturer to produce than the older type of light unit, which is fitted separately to the car. Read more

Fixing a simple light cluster

Illumination for the rear number plate is a legal requirement, though the location of the bulb differs between different models. Common fitting positions include the rear bumper (below), the side of the number plate or the bodywork. Removing a number plate light is basically much the same as for other light units. The light housing surrounding the bulb may have the lens built into it and be simply removed by releasing its securing screws. Read more

Fitting new high-tension leads

The high-tension leads from the coil to the distributor and from there to the plugs may start to deteriorate after long service, causing bad starting, misfiring and radio interference. Read more

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