Vehicle Electrical Systems and Components: A Basic Guide

Buyers Guide & Tips

Back in the day, and I’m referring to the pre-30s/40s automotive era; vehicles’ circuits were simple, containing only a few basic interlays such as lighting, wiper, etc., but over time vehicular circuitry have gotten immense upgrades which have in turn greatly increased their overall complexity – thereby making the understanding of said electrical systems, a bit challenging. 

However, if the electrical system is approached logically, it becomes less of a headache. In this guide, the basics of an electrical system are explained in simple terms. It is essential to know the basics of car electrical systems and how they work, so below is the explanation of a car’s electrical system and how it works. You will learn the basics of a car’s electrical system, vehicle electrics, working parts, and basic terminologies; which are practically used in cars’ electrical systems.  

A car’s electrical system is composed of a wiring harness and electrical components. It consists of several smaller, sub-electrical systems such as the ignition system, charging system, starting system, fuel system, lighting system, etc., which work together harmoniously. In all sub-electrical systems, one thing is a must, and that is the need for voltage which is necessary to operate the electrical components. 

The car’s electrical system is a bit like your body’s blood circulatory system, the primary function of your blood is to provide oxygen and nutrients to the body’s cells and tissues. Similarly, the primary function of the electrical system is to provide voltage to all the electrical components in a vehicle. 

Vehicle Electrics 

Vehicle electrics is the system of electric wiring and parts in a vehicle. The vehicle electrics interconnect all of the car’s electrical parts with each other by carrying electric current and voltage to all the parts such as various computers, sensors, actuators, motors, gauges, power windows, radio, headlights, sunroof, starter motor, and many other electrical components. All the electrical components receive voltage from the battery and return it to the battery. 


The battery is the fundamental source of power in a vehicle’s electrical system that provides electrical current to all electrical components when the engine is OFF. With the engine running, all the electrical components receive energy from the alternators. This is because the alternator produces a higher current than the battery, that’s why it can successfully charge the battery as well supply current to all the other electrical needs of the car while the engine is running. 

How Car Electrical Systems Work 

As previously stated, a car’s electrical system works by providing voltage which is necessary to operate all its electrical components. Without voltage, the electrical system is only just a bunch of wires.  

Sub-Systems Of A Car’s Electrical System 

A car’s electrical system is composed of many sub-electrical systems. Below are the common sub-electrical systems, which are: 

1. Charging System 

2. Ignition System 

3. Starting System 

4. Fuel System 

1. Charging System 

The alternator is the main component of the charging system. It supplies the charge to the battery and accessories. The charging system provides electricity to your car’s electrical system. It provides the current to your car’s electrical system and components – such as starting system, ignition system, fuel system, lighting system, radio, air conditioner, washer pump, etc. 

The battery stores the electrical current and initially provides the current to the car’s electrical system when the engine is OFF. When the engine has been started and the alternator starts to produce the electrical current, that current starts to flow from the alternator onwards to the car’s entire electrical system. 

2. Ignition System 

The function of the Ignition System is to provide a continuous spark to the spark plug in the compression stroke of the gasoline engine cylinders. The ignition system’s job is to ignite the air-fuel mixture in a petrol engine cylinder. 

The ignition system consists of many components such as ignition coils, spark plugs, battery, fuse, and relay. The ignition coil converts the normal battery voltage to a high voltage pulse that goes into the engine cylinder to ignite the air-fuel mixture. 

It is worth noting that diesel engines do not have the classic ignition system; instead in a diesel engine, the air-fuel mixture gets ignited when it is compressed to such an extent that it heats up and ignites in the combustion chamber. 

3. Starting System 

The starting system is an electrical system that works on the principle of converting electrical energy into mechanical energy. Previously, a mechanical hand crank was used to start up a car but in 1912, the electrical starting system was introduced to start a car. 

The function of the starting system is to provide an engine start. The starter motor is the main basic component in the starting system. It uses electrical energy and converts it into rotational energy. 

4. Fuel System 

The fuel system is an electrical system that provides fuel to the engine cylinder. In the past, the fuel system was mechanical in which a mechanical fuel pump was used to send the fuel to the engine cylinder. 

However, due to advancements in technology, the fuel system is now able to operate electrically. The fuel tank stores the fuel that is pumped by the fuel pump through fuel pipelines to the engine cylinder. A fuel system consists of a fuel pump, fuel filter, inertia safety switch, fuse, and relay. 

Car Electrical Parts 

Every part in a vehicle that operates electrically or electronically is called a vehicle’s electrical system part. 

In the early generation of vehicles, the majority of components were mechanical and simple. With time, the vehicle’s parts got updated, and components started to operate electrically or electronically. 

The reason for operating the parts electrically and electronically is for ease of operation and precision control. A car’s electrical system has hundreds of electrical and electronic parts. Let’s have a look at five of them, namely: 

1. Fuse 

2. Relay 

3. Battery 

4. Alternator 

5. Starter Motor 

1. Fuse 

The fuse is the most essential part of a car’s electrical system. It is a safety device used to protect the electrical wiring from damage in the event of a short circuit. 

A fuse kills itself when the current exceeds its pre-determined current value. Ideally, every electrical circuit in a car should have a fuse to protect the circuit from damage in the unfortunate event of an overload. The fuse’s working principle is based on the heating effect of the current. It is designed to blow up in an overload situation and break the connection. 

A fuse contains a metal element and two terminals encased by a plastic housing body. The metal element is a resistive material made from zinc, copper, or aluminum, which produces heat when the current flows through it. 

When the current exceeds its predetermined current value, too much heat is produced in the fuse element which causes it to blow the fuse. The fuse element is soldered to the fuse terminals. Fuses are located in the fuse box inside the cabin or outside in the engine compartment. Some aftermarket circuits use an inline fuse. 

2. Relay 

The relay is a very important car electrical system part. It can control many electrical circuits with a single trigger. 

A relay is an electromagnetic switch used to connect and disconnect the electrical circuit. It is mostly used in heavy circuits, which consume a tremendous amount of current. The relay controls a large amount of current by using only a small amount to avoid burden on the wires. 

The engine cooling fan uses a relay to provide a high amount of current to the cooling fan for maximum cooling. Similarly, the car’s air conditioner, ABS Motor, headlight, starter motor, horn, etc., use a relay to provide the maximum current to the components and avoid load on the wires. Relays are fitted alongside fuses in the fuse box. 

Usually, there are three types of relays used in the automobile industry – they are three-pin, four-pin, and five-pin Relays. The four and five-pin relays are very common in vehicles. 

3. Battery 

The battery is the heart and most necessary part of a car’s electrical system. It provides life to the electrical system. It is the basic source of electricity in the car’s electrical system. It provides electric current through wires to all the electrical components. 

The battery is an electrochemical device and a power bank, which stores the electrical current. It stores the electric current in chemical form and converts it into electrical (electric current) form when required. With the engine OFF, the battery provides the current to all the electrical circuits, including ignition and starting circuit to start up the engine. And when the engine starts, the alternator supplies current to all the electrical circuits. 

The lead-Acid battery is one of the most common batteries in the car. It contains lead plates submerged in sulfuric acid. 

The battery acts as a reservoir when the current demand is higher than what the alternator produces. The battery also provides additional current to the electrical circuits. Similarly, the battery acts as a stabiliser, it regulates damaging voltage spikes when the engine is running. 

4. Alternator 

The alternator is one of the essential parts of the car’s electrical system. The alternator is an electro-mechanical device, which converts mechanical energy into electrical energy driven by the engine belt. The alternators produce AC current that is converted to DC current by a rectifier (also known as a diode bridge which consists of six diodes). 

The alternator provides electrical power to the car’s electrical system and battery while the engine is running. It initially needs the current (which the battery produces at first) to start producing the electric current. This initial current is known as excitation, in which the alternator is excited by the battery ignition switch through the exciter wire. 

The type of alternator, which needs an excitation from the battery to start producing electric current is called a non-self-exciting alternator. Some alternators do not need an excitation current; those types of alternators are called self-exciting alternators. 

A fully charged battery gives almost 12.6 volts (with the engine off), and a good working alternator produces almost 14 to 14.6 volts. To charge the battery, an alternator must produce a higher voltage than the battery. 

5. Starter Motor 

The starter motor is an electrical component of the car’s electrical system that helps in starting the car. 

The starter motor, also called a starter or self-starter. It’s a device used to crank the engine. It converts electrical energy into mechanical energy in an IC (Internal Combustion) engine and is usually mounted on the back of the engine casing, or in front of the transmission housing. 

The starter motor consists of several parts such as armature, commutator, brushes, pinion gear, overrunning clutch, field coil or permanent magnet, and planetary gear set. All these parts combine to create the starter motor. A solenoid fits on the starter motor assembly, which acts as an electromagnetic switch. The solenoid connects and disconnects the battery to the starter motor. 

With this, you now have a good idea about how a car’s electrical system functions, and its various parts. Thanks for reading as always. 

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