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 contact (live). Fix crocodile clips to the wire ends.

Guides that use

Checking windscreen wipers and washers

How the washer system works Fluid for screen washing is drawn by a pump from the washer bottle a...

Fitting a new windscreen-washer motor

The motor and pump are usually a single unit, the pump being a simple device. If the non-return ...

How to fix a dynamo

A typical dynamo The electrical connections from a dynamo are on the rear endplate. Current gene...

Car horn not working?

Adjusting a windtone horn Adjusting the screw and locknut. Double live terminal for connection t...

How to fix a car fan

Checking the circuit and motor for faults Look at the fuse box for a blown fuse. If the fuses...

How to test electrical circuits

A typical lighting circuit Power for the cars ancillary circuits comes from the live side of the...

Checking a starter circuit

Inertia starter An inertia starter has the solenoid mounted elsewhere in the engine compartment,...

Removing and refitting the distributor

Before removing the distributor cap, tag the lead to the cylinder used for timing and mark its p...

Working on the wiring system

The electrical wiring in a car is a system of colour-coded wires called the loom (See ). Where s...

Checking the instruments

Typical instrument panel The back of the instrument panel Warning lights and instrument bulbs ma...

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

Sender unit Some sender units have a bayonet fitting with lugs in the flange. Petrol tank The ta...

Checking the low-tension circuit

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

Adjusting the static timing

Setting top dead centre Align the timing notch on the crankshaft pulley with the marks on the en...

Testing and replacing a flasher unit

The switch on the steering column On some modern cars with multi-function switches on the steeri...

Servicing the windscreen-wiper mechanism

A pushrod linkage The wiper arm may be held to its spindle by a hexagonal nut, usually hidden by...