Electrical Faults

Your car has many electrical components and electronic devices – it just can’t operate without them. Some of the electronics are for convenience, such as heated seats, electric windows and sunroof or sound system. Others are essential for the operation of the vehicle, such as the ignition system, wiper motors and headlights. If any of the electronics in your car have stopped working, it may be something as simple as a blown fuse, or it may be a more complex problem. Whatever the apparent cause of the electrical fault, it needs to be checked out by someone who really understands a vehicle’s electrical system. The AutoMend network gives you access to highly skilled auto repair and maintenance specialists all across the UK. Our members are all trusted professionals, who are either based in local garages or out on the road as mobile mechanics, so they are never far away when you need help with electrical fault repairs. Whether you are in Wales, Scotland, Ireland or England, you can call on our mechanics for rapid diagnostics and repairs to keep your car safely on the road.


Whatever the model of car you drive, they all have a very similar electrical system, which basically comprises a wiring harness connected to a battery. The wiring harness is a group of wires of different thicknesses, contained within plastic coverings, that snake about all over the car. All the car’s various electrical systems are connected to the wiring harness, either directly or through separate connecting wires, and are provided with the power they need to operate by the battery.

The car’s various circuits are all protected by fuses, which are designed to blow if the load becomes too great for the wiring to cope with. Some electrical devices impose a heavy drain on the electrical system – these include the starter motor. The wiring which connects heavy usage devices to the battery is itself thick, heavy duty cable, and is protected by high-amperage fuses. Where there is a lesser drain, the wiring is usually thinner and less substantial, with correspondingly lower amperage fuses.

In a car with a traditional combustion engine, the battery provides power to systems that need to operate when the engine is not running. In an electric car (or a hybrid car in electric mode), the battery powers the engine as well as the electrical systems.


The most frequently encountered problems with a car’s electrical system are open circuits, short circuits and low battery power.

Open circuit

In an open circuit, voltage is unable to flow because there is a broken connection. It is possible that a wire has become damaged due to friction or flying debris, causing the core to break. Another cause of open circuits is a blown fuse, or perhaps a connection that has come unplugged. A visual inspection can sometimes spot the problem, especially if it’s something that has come unplugged. Otherwise, it will be necessary to test out the circuit using a meter to pinpoint the problem.

Short circuit

A short circuit is a connection that shouldn’t be connected. A prime cause of short circuits is where the insulator of a wire has worn away, and the internal wire core is now touching something metal. Short circuits can in certain circumstances lead to fires, which is why the electrical systems are protected by fuses.

Low battery voltage

Car batteries have to work very hard, and they don’t last forever. When your car is in use, the battery is constantly being discharged and charged up again by the alternator. When you start your car, the starter motor pulls a great deal of power from the battery very quickly.

In cold wintry weather, the battery can run down quickly because you need to use your lights most of the time, and the car heater will be on. If your car has air conditioning, this also puts a tremendous strain on the battery. Over time, the battery will take longer to charge up, and will eventually fail to hold enough charge to start your car. Running with low battery voltage can cause problems within the electrical system which may leave you stranded.



A car fuse is most usually made up of a piece of wire, which is enclosed within a heatproof outer case, which can be made of glass or some other fire-resistant material. The aim of the fuse is to protect the particular circuit and its components from damage if a power surge occurs. A circuit that is not protected by a suitable fuse may overheat which can damage the outer coating of the wiring and may cause fires.

The choice of the right thickness of wire within the fuse is critical to the safety of the circuit. The fuse wire needs to be thick enough to carry the current that usually runs through the circuit when everything is operating normally, but thin enough to melt or ‘blow’ immediately if excess current occurs. The size of the fuse wire is rated in amps.

Your car will probably have many sets of fuses throughout the electrical system – they are designed to isolate the various circuits so that if one fuse blows, it doesn’t stop the whole vehicle. Some fuses are located within a central fuse box, which may be under the dashboard or in some other accessible place such as the driver’s footwell. As well as the fuse box, there may be other fuses (called line fuses) located within the wiring of the various circuits.

If a fuse blows, it is a good idea to do a visual check to see if there is anything obviously wrong, before fitting a new fuse. The new fuse must be the correct amp rating for the circuit. If the new fuse blows, you have an electrical fault that needs to be checked out by an expert. Electrical faults are dangerous – there is always a risk of fire, so don’t delay in getting problems checked out as soon as possible.


There are several different types of fuses used in modern cars. It is often possible to tell if they have blown by a visual check. Look at the fuse wire against the light, checking for breaks. Signs of charring or burning are also an indicator that the fuse has blown.

Blade fuse

These types of fuse are the ones most frequently encountered in the UK. They have a coloured rectangular top, with two blade-type metal connectors that push into slots in the fuse holder. The fuse wire is usually visible within the coloured coating.

Barrel fuse

Another fuse type is a barrel-shaped fuse with a clear glass tube and two metal end caps. The fuse wire is visible within the glass tube.

Bar fuse

A third type is associated with continental cars, and is a solid coloured bar, with a metal strip on one side which is designed to melt when under excessive loads.


Finding the fuse box can be the first challenge – refer to the owner’s handbook for help. Most fuses simply push into the fuse holder, which has a pair of spring-clip contacts. Pull out the old fuse and then clean up the fuse holder clips with a little fine emery paper if there is any corrosion or dirt visible.

Take a new fuse of the correct amp rating (again, refer to the owner’s handbook). Getting the right amp rating is crucial, as the fuse is a key safety feature of the circuit. Put too big a fuse into a circuit, and the fuse won’t blow if excess load occurs – the circuit wiring itself may end up being damaged, or it may even catch fire. Too small a fuse, and the circuit will probably blow straight away. Give the connectors or end caps a clean-up with the emery paper to ensure a good connection. Push in the new fuse and try the circuit to see if it is working.

If the circuit is working with the new fuse in place, the problem was the old fuse. If the circuit does not work with the new fuse, you need to know if the problem is the circuit itself. If there is a fuse of the same rating in a circuit that is working try the problem circuit with that fuse. If the circuit still doesn’t work, then the fuse is not the problem, and you will need to call on some expert help from the AutoMend network.


It couldn’t be easier - AutoMend is a simple way for drivers to get access to a huge variety of mechanics offering vehicle maintenance and repair services. With access to over 9,000 locations and mobile mechanics available, wherever in the UK you happen to be, we will have a local representative on hand. What’s more, they all hold industry approvals.

Electrical faults can be tricky to diagnose and repair, so you need to be confident that whoever you entrust with this vital task is up to the job and won’t charge the earth. To get the repair process started, we simply ask for your postcode / location, then your vehicle make and the nature of the repair. Once you have entered the information, we will provide a list of garages and mobile mechanics, along with their phone numbers and how far away from you they are. You can call up your preferred garage for a chat about your requirements, or simply ask for online quotes, free of charge and no-obligation.
You don’t need to spend time and effort searching online for ‘car electrical repairs near me’, let our network provide you with the best deals around. It’s quick and easy, and you will be delighted by the prices and choice of services on offer from our members.