Electrical systems in cars have evolved from their rudimentary beginnings more than a century ago, to systems that today boast hundreds of different parts and miles of wiring. Features like cruise control, cold air from the A/C, ABS, and power windows have existed for decades and are now complemented by start/stop systems, traffic sign recognition, and auto emergency braking. Of course, this is just the tip of the iceberg, and vehicles vary greatly as to the different electrics and electronics they have on board.
Automotive electrical systems are what start the car, control complex engine and drivetrain units, as well as basic things like lights and wipers. With so many auto electrical parts responsible for a multitude of different driving systems, all drivers should have a basic understanding of vehicle electrics and how they work.
Electrics in vehicles revolves around major components like the battery and alternator, responsible for providing the voltage to power each part, and wiring and connectors to conduct that voltage to where it is needed. This is a simple take on things, and diagrams depicting the sheer complexity of wiring and parts in high-end performance and luxury cars loaded with features are true artworks. They also show how much thought has gone into improving all things driving and everything we take for granted even before we turn the key.
If ever the need arises to shop for auto electrical parts, here’s what you should know.
The Battery
The battery is the central part of any electrical system. It provides the current that powers all vehicle electrical components, including the ignition and starter that gets the engine going. Current is produced through a chemical reaction inside the battery cells and flows from the battery’s positive terminal, powers the electrical part, and completes the circuit to the negative terminal.
Most car batteries are 12 Volt Flooded Lead Acid affairs. They’re also called SLI (Starter, Lighting, and Ignition) batteries. A higher-performance version, called EFB (Enhanced Flooded Battery) has higher discharge rates and longer life cycles often used as a replacement for simple lead-acid batteries, and is regularly found in cars with simple start/stop systems. Advanced start/stop systems and cars with regenerative braking may also run on AGM (Absorbent Glass Mat) batteries, that can supply the consistent high power demands that ordinary lead-acid batteries can’t.
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Lithium-Ion (Li-Ion) batteries are those found in EVs (along with a lead-acid battery as a backup), whereas hybrid cars use Nickel-Metal Hydride (Ni-MH) with even higher discharge rates than even Li-Ion batteries.
Batteries also come in different sizes and ampere hour ratings. Look for higher cold cranking amp numbers (the amount of current that a battery can deliver for 30 seconds at 0°F to maintain a voltage of 7.2V), if you live in colder climates. Also, consider the ‘reserve capacity’ or how long the battery can run the vehicle when the charging system fails.
The Alternator
Alternators are the car electrical components that produce electricity once the engine is running. They are often bolted onto the engine and connected with a pulley to the crankshaft that gives the alternator the mechanical energy to spin. Alternators are tasked to produce current for a variety of electrical systems, including the car battery. In fact, the battery is recharged the longer the engine (and the alternator with it) is spinning.
Inside the alternator you’ll find two basic parts – stators and rotors. Stators are the stationary parts containing three groups of coils, and the rotor is the part that spins with the crankshaft.
Inside the rotor are magnets, that induce a magnetic field and AC current in the stator coils. This is converted to DC current by a rectifier to run various electrical components in the vehicle. Since the voltage produced by the alternator is higher (14 or 14.6V) than a fully charged battery (at 12.6V), the battery is charged by current flowing from high to low electrical pressure. Overcharging the battery or supplying too high voltage to other parts is avoided with a voltage regulator found within the alternator.
The Starter
The electrical part tasked to get the engine turning is aptly called the starter motor. This is attached at the end of the crankshaft with a flywheel and pinion gears. The electromagnetic windings inside the starter engage a rod in the gears and this turns the crankshaft. The initial charge is provided from the battery with the key turned halfway (ignition) and a solenoid (a type of relay) inside the starter disconnects the current once the engine is turning.
Wiring
Current from the battery and alternator is fed to dozens of electrical parts and vehicle systems like the lighting, fueling, air-conditioning and various control modules and sensors with wiring. Some wires transmit signals from sensors and switches and require low current, whereas other systems like the air-conditioning require large amounts of current (roughly 100 amps depending on the vehicle).
Wires need to be sourced in the right length (to reduce electrical resistance), conductors (copper is the most common material here), and gauge or diameter – with thicker wires able to handle more current and thus have less resistance. In addition, wires can also be bundled into wiring harnesses and have different types of connectors to simplify the connection of larger vehicle components.
Fuses
To protect the wires (and electrical components they connect), fuses cut the connection when there is a current overload leading to overheating or short circuits. Ideally, every vehicle’s electrical circuit will be fitted with its own fuse. This consists of a resistive metal element and two terminals housed in a plastic casing. When the current exceeds a pre-set value, the resulting heat causes the fuse to blow and cut the circuit.
Fuses are often bundled in two fuse panels. One is in the engine compartment and houses fuses for things like cooling fans, fueling, and ABS. The other is under the dash on the driver’s side and has fuses for windows, lights, the radio, and other electrical devices in the cabin.
Relays
These are electronic or electromagnetic switches used to turn an electrical component on or off. Relays consist of two halves –a low amperage circuit fed current from the battery and turns on the second half -a high amperage circuit that runs things needing higher current like the aircon, lights, or cooling fans. Some relays can have a delayed timing function, and turn off a circuit after a certain period, as in rear window defrosters or starter motors. You’ll find relays in the same location as fuses, that is in fuse panel boxes.
Control Modules and Sensors
With the complexity of today’s vehicles, auto electrical parts are also tasked to control various subsystems. Control modules like the Engine Control Module (ECM) are responsible for fueling, ignition timing, cam timing, and emissions. Other controllers work with sensors placed around the vehicle to measure things like coolant temperature, body roll, vehicle height, tire pressure, moisture levels, and more.
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Sourcing Electrical Parts
Vehicle makers rely on dozens of third-party manufacturers for essential or more specific parts, including wiring and electrics. Compatibility here is key, and you’ll want auto electrical products that suit the model and make. Before making any purchases, check the vehicle identification number (VIN).
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