The electrical system of a car is a closed circuit with an independent power source the battery. It operates on a small fraction of the power of a household circuit.

Current flows along a single cable from the battery to the component being powered, and back to the battery through the car's metal body. The body is connected to the earth terminal of the battery by a thick cable.

Earth-return system
In a negative (-) earth-return system, the current flows from the positive (+) terminal to the component being operated. The component is earthed to the car body, which is earthed to the negative (-) terminal of the battery.

This type of circuit is called an earth-return system any part of it connected to the car body is said to be earthed.

The strength of the current is measured in amperes (amps); the pressure that drives it round the circuit is called voltage (volts). Modern cars have a 12 volt battery. Its capacity is measured in amp/hours. A 56 amp/hour battery should be able to deliver a current of 1 amp for 56 hours, or 2 amps for 28 hours.

If the battery voltage drops, less current flows, and eventually there is not enough to make the components work.

A circuit usually includes more than one component, such as bulbs in the lighting circuits. It matters whether they are connected in series one after the other or in parallel side by side.

A headlamp bulb, for example, is designed to have a degree of resistance so that it consumes a certain current to glow normally.

But there are at least two headlamps in the circuit. If they were connected in series, electric current would have to go through one headlamp to get to the other.

The current would encounter the resistance twice, and the double resistance would halve the current, so that the bulbs would glow only feebly.

Connecting the bulbs in parallel means that electricity goes through each bulb only once.

Some components must be connected in series. For example, the sender in the fuel tank varies its resistance according to the amount of fuel in the tank, and 'sends' a small electrical current to the fuel gauge.

The two components are connected in series so that the varying resistance in the sender will affect the position of the needle on the gauge.


Content this app :

- Wiring Diagram
- Wiring Diagram Car
- Electrical Wiring Car
- etc