Car Electrical System and Auto Electricians

I had a problem with my car which is over ten years old - my left indicator and reverse lights did not work. I did not have a great knowledge about vehicle electrical systems but I am did manage to find the problem and fix it with an understanding of the components that make up the electrical system in my car.

We need to know a little about the system before we can start to fully diagnose what's going wrong.

The battery of a car

The battery is your cars main source of electrical energy stored in a chemical form that provides between a 12 to 12.6 volts potential difference to all your electrical components on your car. It has 2 terminals a positive and negative.

The positive Terminal marked "+" (plus) or commonly called "hot" has a red or black battery cable connected to it.

The negative Terminal marked "-" (minus) or commonly called "ground." The negative battery cable is usually a two wire black cable. The smaller diameter cable is connected to the sheet metal for the Accessory Ground. The larger diameter wire is connected to the engine block for the Engine Ground.

One post is marked "+" (positive) or "hot" side and has a red or black battery cable connected to it. The Junction Block is a voltage side common connection point used on many vehicles. It is located in the engine compartment near the battery. The negative battery post is marked "-" (minus) and is called "ground." The negative battery cable is usually a two wire black cable. The smaller diameter cable is connected to the sheet metal for the Accessory Ground. The larger diameter wire is connected to the engine block for the Engine Ground.

Your Car alternator

An alternator charges your battery and powers your car's electric system when the engine is running.

Quick Example

So if I am parked and waiting for someone outside of Milton Keynes central shopping centre and my engine is running and I am listening to 5 live on my radio my alternator is powering my radio. If I turn off my engine and still listen to 5 live my radio is being powered by my battery. Battery and alternator connection.

If you look at your batteries positive terminal marked "+", you should find a thick wire connecting the terminal to the alternator. This is your alternator positive terminal normally marked "B+". This cable carries charge from the alternator to the battery. The alternators housing or casing acts as the negative Terminal (Ground) and is connected through the engine ground and the engine block.

Voltage Regulator

This regulates the voltage going from the alternator to the battery, it will keep the voltage of the battery between 13.5 volts to 14.5 volts.

Checking your battery and alternator

You can test your battery and alternator with a Digital Multimeter.

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