Electrical systems

The dynamo is a robust and simple type of generator which was fitted to many earlier cars. Most modern cars are fitted with an alternator . Read more

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

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

If your car's instrument panel includes an ammeter , it will tell you how well the charging system is working - the difference between the charge going into the battery and the power being used from it. Read more

On cars with dynamos, faults in the control box show up in various ways, some of which are described in Testing a dynamo and checking output . Read more

Wear on the carbon brushes and commutator is the most common cause of dynamo failure. Read more

Drive belts always stretch a little in use, because of the strains put on them by driving the water pump and generator , as well as the fan itself if it is in the system. Age and continual flexing also cause belts to crack and deteriorate. Read more

A faint click or total silence when the starter key is turned usually means that the battery is almost or completely flat. If, however, the battery is fully charged, the trouble is probably in the circuit between the battery and starter. Read more

Alternators have replaced dynamos as generators on modern cars; they can produce more current . Read more

The carbon brushes are a sliding fit in oblong holders on the dynamo endplate. Coiled springs bear against the tops of the brushes to hold them in contact with the commutator . Read more

The most common reason for removing a dynamo pulley is to fit it on a new dynamo — most replacement dynamos are supplied without one. Read more

Unlike dynamo brushes , alternator brushes normally last for several years. Electrical arcing between brushes and commutator , a major cause of dynamo wear, is far less common. Read more

When you have tested the charging system of a car fitted with an alternator , and the checks in How to test a car battery point to a fault in the voltage regulator , make sure that you need to replace it. The fault may be elsewhere. Read more

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

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

Alternators are powerful enough to cope with the demand for current made by a modern car's electrics, but dynamos often are not. So if your car has a dynamo, and its output is inadequate, it makes sense to swap a dynamo for an alternator. Read more

It is essential to keep your car lights in good working order all the time. Apart from being dangerous, a defective light may also be illegal. If you do find a defective light unit, and you know the bulb is not at fault, the problem may lie in the light unit itself. Read more