An overview of the electrical system

Someone once said a car needs only two things to run — fuel and electricity. Well, OK, three things, if you count air. But the point is this: A car depends on only these three things for basic operation.

“How can that be?” you ask. “Today’s cars are so complicated.” Well, compare an old car with a modern one. If you look beyond the obvious, what do you find? The basics are the same. Nowadays, it’s only the application that’s more complicated. Take electricity.

The essential electrical components in old cars and new ones are practically the same — ignition, starter, generator, battery and lights. But today’s cars also come equipped with electric wipers, electric gauges, electric windows — even electric mirrors. Most of today’s extras are just that — extras. But all these components have one thing in common. They all need electricity to operate.

So, before getting into the specifics of electrical theory and how to wire your car, let’s take a brief overview of the car’s electrical system.

Brief overview of the car’s electrical system

The electrical system can be divided into three major parts:

  • electrical sources
  • electrical loads — users of electricity
  • electrical paths

Electrical sources consist of the battery, which stores electricity for starting the engine, and the generator or alternator, which provides electricity when the engine is running. Except in cases of extreme overload, a correctly adjusted charging system will produce enough power to operate all the electrical devices in the car, with enough extra to recharge the battery.

Electrical loads include all the devices on the car that require electricity for operation. Some examples are the ignition system, windshield-wiper motor, heater-blower motor, horn, radio or tape deck, and lights. By the way, don’t underestimate the electrical loads created by lights. It’s common for a car to have more lights than all the other loads combined — 20 to 30 lights can be found in a modern car. And, in some race-car applications, such as rally cars, off-road racers, and IMSA GTO and GTP cars, the electrical load from driving lights can be quadruple that of conventional lighting systems.

Electrical paths include wires, of course. But a car’s steel body and frame are also paths. They’re used as the return path, or ground, between loads and the battery. And the various switches in the system can be included in the path category. Switches are located in the electrical path to act as a sort of gate, permitting electricity to pass or to hold it back, as required.

Together, these three parts form electrical circuits, which enable electricity to perform useful work.

It’s remotely possible for you to successfully wire a car without any idea whatsoever about electrical theory. But don’t try it.

Why? It would be similar to taking a trip without a road map. You may have an idea of where you want to go, but no clear-cut idea of how to get there. Or, perhaps more important, you don’t know what’s involved in making the trip. So, I strongly suggest you take the time to learn basic electrical theory before you try to wire your car.