Use a 6-12 volt circuit tester for checking a car circuit. It has a short metal probe, and the translucent insulated handle contains a 12 volt bulb and has a length of cable attached that can be clipped to the car body as an earth. The probe is used to test the live side of the circuit. Where there is current, the bulb lights up.

To make a simple test lamp, use a single filament bulb and two lengths of low-current carrying wire. Solder one length to the bulb basecap metal (earth), the other to the single centre (live). Fix crocodile clips to the wire ends.

Guides that use

Checking windscreen wipers and washers

Windscreen washers and wipers must, by law, be in working order. Keep the washer bottle topped u...

Fitting a new windscreen-washer motor

Cars with electrically operated windscreen washers sometimes have a switch controlling the motor...

How to fix a dynamo

Wear on the carbon brushes and commutator is the most common cause of dynamo failure. Normally t...

Car horn not working?

Cars are usually fitted with a high-frequency (HF) or windtone horn as standard equipment, norma...

How to fix a car fan

Electric radiator-fan motors are switched on either by the ignition switch - and run while the e...

How to test electrical circuits

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

Checking a starter circuit

If the starter does not turn the engine although the car battery is in good condition, the fault...

Removing and refitting the distributor

On some cars, because of limited space, the only way of replacing the -breaker points or ...

Working on the wiring system

The electrical wiring in a car is a system of colour-coded wires called the loom. Where several w...

Checking the instruments

A car usually has up to six main instruments — speedometer and tachometer (rev counter); fuel, o...

Checking headlamps and lights

It is an offence in law not to have all obligatory lights working. Check them frequently, especi...

Checking and replacing a fuel sender unit

If the fuel gauge reads empty when you know there is fuel in the tank, the cause may be...

Checking the low-tension circuit

The low-tension (LT), or primary-ignition, circuit consists of the battery, ignition switch, con...

Adjusting the static timing

The timing mechanism in the ignition system causes the sparkplug to fire in each cylinder just b...

Testing and replacing a flasher unit

There are two basic types of flasher unit. One is operated by a piece of wire or a bimetallic str...

Servicing the windscreen-wiper mechanism

The windscreen-wiper mechanism needs little maintenance. At service intervals drip a little oil d...

How to fix a car heater

The car's heating system consists essentially of a motor-driven fan to blow warm air from the en...

Fixing a reversing light

Reversing lights are not generally a legal requirement but they are useful. They serve two purpo...