A Guide to Automotive Electrical System

Cars have evolved at a breakneck pace, morphing from the clunky and slow behemoths of a century ago to agile speed machines that will see you flying past the legal speed limit in the blink of an eye. Today, cars are not only faster, safer, and much easier to drive, but they also provide a dose of luxury and convenience. Much of this is down to the multitude of electrical systems, ranging from multi-zone air conditioning, heated and cooled seats and power windows, to auto lights and wipers, sign recognition systems, and safety features such as ABS and rear collision warning. The goal is to travel in comfort and with minimal risk. 

The tech on board varies among vehicles in different price brackets. But common in every car is the system that starts the engine, and controls various engine properties such as fuelling as well as basic systems such as braking. Major components like batteries and alternators provide the initial power for all the vehicle electrics. These are supplemented with wiring and connectors to get that power to where it’s needed, such as the slew of different sensors.

Car Electrics – The Basics

Batteries, alternators, and starter motors are the basic electrical components in cars with internal combustion engines. They provide the initial power to get the engine going, and all parts rely on electricity to work. Connecting these is miles of wiring and dozens of protective and actuation devices such as fuses and relays. The rich list of auto electrical supplies is also populated by numerous sensors monitoring different vehicle vitals. 

The Battery

Batteries are the heart of your car’s electrical system and provide the current needed for everything else to work. They supply power to the starter which turns the crank to get the engine going, and the alternator to provide power once the car is on. This happens during a chemical reaction inside the battery cells, with power flowing from the positive terminal to the required component, and the circuit terminates in the negative terminal. 

There are a variety of battery types. The most common are 12-Volt Flooded Lead Acid. These are reliable, efficient, inexpensive, and generally low maintenance. In cars with start/stop ignition, an advanced version, known as EFB (Enhanced Flooded Battery) and AGM (Absorbent Glass Mat) are better is delivering higher discharge rates and more consistent power supply without affecting total cycle rates. 

Lithium batteries are found in EVs, and in varying power output, while hybrid cars rely on Nickel-Metal Hydride (Ni-MH) for initial get up and go, as well as regenerative braking. Both types have better discharge rates, meaning they’re more efficient and will last longer, and fare better against high temperatures, in addition to being lighter and smaller (for the same output). 

When looking for a replacement battery, go by Ampere Hour (Ah) ratings as well as the reserve capacity to charge vehicle systems if the alternator is defective. 

The Alternator and Starter Motor

This is the auto electrical part that produces electricity with the engine running. The alternator is connected with a pulley to the crankshaft and this provides the inertia to spin. The part powers all the electrical systems in the vehicle and recharges the battery. This is possible by producing a higher voltage than a fully charged battery. 

Starter motors do exactly what they say on the box. They provide the energy to turn the engine over, by rotating the crankshaft. The initial charge is provided by the battery, and once the engine is up and running, a system of relays or solenoids cuts the current. 

Wiring, Fuses and Relays

Wires in different lengths and gauges (thickness) connect the battery and alternator with the dozens of different auto electrical supplies and parts in the vehicle. They send generated power to run things like the windows, wipers, ECU, and power-hungry systems like heating and air-conditioning. The current (and wire gauge)  will be different according to the connected part. Wires terminate in connectors making connecting simpler and faster. For a cleaner look, wiring from several related systems is bundled in wiring harnesses. 

Fuses are the electrical parts that are tasked to cut the current in the event of an electrical fault. This way they protect both the components and wiring. Often, fuses are located in fuses boxes, with one in the engine bay controlling the current in parts like cooling fans and injectors. Another is on the driver’s side of the cabin and houses fuses for windows, wipers, lights, and other interior parts and systems. 

Relays are a type of electromagnetic switch that is tasked to turn an auto electrical part on or off. Often they control the power supply to parts requiring more power. Some relays also come with a delay function, for things like the rear window defroster and starter motor. They too are located in the same boxes as fuses. 

Different Vehicle Sensors

All cars today have a variety of sensors for more precise control over different vehicle systems. Sensors monitor what is going on inside and outside the car, and provide data to the ECU and vehicle computers. These can then make any needed changes. 

The aim of sensors is to improve engine performance and efficiency, reduce overall emissions and fuel use, increase ride quality and comfort, and maintain safety. There are a dozen or so sensors in modern cars. They oversee variables like temperature, pressure, airflow and air density, ambient light, humidity, proximity to other vehicles, vehicle height, and more. 

More common types are Oxygen sensors, located in the exhaust and monitor air and fuel ratios in combusted mixtures; air and fuel temperature sensors for efficient combustion, MAF and MAP sensors for sufficient air supply; parking and ultrasonic sensors for safer reversing; proximity sensors for cruise control, ABS sensors for safer braking… the list goes on. Generally, the newer the car the more sensors it is likely to have. 

Common Electrical Faults in Cars 

The majority of car issues can be diagnosed using an OBDII code reader or scanner. Apart from blown fuses, most scanners can pinpoint where an electrical fault originated and what the issue is. In most cases, you’ll be looking at depleted or dead batteries and difficulty starting the car or flickering lights, alternator problems leading to lower than usual voltage, and issues with the starter motor. Minor issues are blown fuses, cutting power and functionality to different parts (stuck windows are a prime example), and faulty relays. Sensors too can fail and will trigger the appropriate light in the dashboard. There can also be damage to the connectors or pins, and fraying in the wiring. Most problems are easy and inexpensive to fix if detected on time.