What Is the Wiring Harness in a Car: Components and Benefits

What is the wiring harness in a car? Cars are large, with an average length of 14.7 feet. Despite this, most of the components that make it work are small.

The wiring harness in a car is responsible for airbags, ABS brakes, climate control, and the engine. Without a wiring harness, none of these features would be possible.

For this reason, it is important to fully understand what a car’s wiring harness does. Next, we answer this question and its usefulness in your automobile.

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What Are Auto Wiring Harnesses?

An auto wiring harness assembles cables, connectors, terminals, and wires that transport electrical power in a car.

Before now, cars were solely mechanical and could run without electricity. But it’ll be a miracle to run a modern car without electricity.

For this reason, auto wiring harnesses are a crucial part of any car engine. Electrical current won’t reach the car’s different electrical components without them.

The car’s ignition system, such as the starter, chassis, and alternator, all need electricity. And they can’t get this electricity without an auto wiring harness to convey them.

But for cars, having an auto wiring harness isn’t enough. The wires and terminals must also be properly connected to the electrical components.

To understand this connection is to know the different wiring harness circuits.

Modern automobile engine

(Modern automobile engine)

Automotive Wiring Harness Circuits

Since automotive wiring harnesses connect to different electrical components, they come with different connection circuits.

Also known as wire lengths, the circuits serve distinct purposes. And a standard automotive wiring harness has 12 of them.

The circuits include:

  1. Dash lights
  2. Gauges
  3. Hazard flasher
  4. Heat and AC
  5. Horn
  6. Parking lights
  7. Radio
  8. Stop lights
  9. Tail lights
  10. Turn signals
  11. Wipers
Automotive wiring harness cables and circuits

(Automotive wiring harness cables and circuits)

From their names, you can easily understand what each circuit does. 

However, many high–end vehicles feature wiring harnesses with more than 12 circuits. Some come with 18 and others with 24. These extra circuits are important because the vehicles come with more electrical components.

If a car has 18 circuits, these are the extras you’ll find:

  1. Electrical fuel pump
  2. Electric fan
  3. High-level stop light
  4. Two power locks
  5. Radio B+ memory

But if the car has 24 circuits, these are extras – in addition to the 18:

  1. Dome light
  2. Trunk light
  3. Glove box light
  4. Clock
  5. Under hood light
Under hood light

(Under hood light)

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Components of an Auto Wiring Harness

Besides circuits, auto wiring harnesses also have various components, including:


The connector component manifests its name: it connects the harness wires to the different circuits and power sources. A typical connector will have a male pug end and a female jack end. Both ends join together to transmit the current.

However, connectors are of different types, depending on the harness. They also come in different materials, with the best ones being brass and copper.

Car electrical cables and wires

(Car electrical cables and wires)


Generally, the work of a fuse is to protect electrical components if something goes wrong. For example, when the current is excessively high. When talking about cars and their wiring harnesses, it’s no different.

The wiring harness fuse features a wire that’ll easily melt at a certain current level. When it melts, it breaks the circuit.

Thus, it stops rouge currents from reaching the car’s electrical components, protecting them.

protect electrical components

(protect electrical components)

Fuse Block

Each circuit in the wiring harness has a separate fuse. That means one fuse going bad won’t affect all components. A fuse block is like a house where you assemble the different fuses. It’s similar to a distribution board.

The wiring harness behind the dashboard

(The wiring harness behind the dashboard)


The relay component of an auto wiring harness works for high current circulation. It’s one of the most important components, drawing power directly from the battery. In contrast, some components draw power from other car system parts. Consequently, the relay component can deliver a powerful current from a low one.


A wiring harness is an assembly of electrical cables or wires. The cables or wires are the components in view here. These are usually copper wires and come in different circuit measurement variants.

For example, the horns and headlight circuits use a 1.5 gauge wire. But the circuits for dome and door lights use a 0.5 gauge wire. It’s critical to confirm the current value of a circuit when purchasing a wire for it.

The electrical worker checks the car wiring

(The electrical worker checks the car wiring)

What Are the Benefits of Automotive Wire Harnesses?

Having an automotive wire harness in your car is better than not. Here are some of the benefits they bring:

  • Less shorting occurrence: with an automotive wire harness, the possibility of circuit shortage is less. Why? Because the harness assembles multiple wires into well-laid bundles. These bundles are non-flexible and not loose.
  • Quick setup: installing a wire harness can be time-taking with the many wires and circuits to connect. However, with an automotive wire harness, you only need to connect a single unit, and all wires will work. Besides making setup easy, you’ll also avoid making wrong connections.
  • Better fuel usage: installing an automotive wire harness will ensure your car optimizes fuel usage. In the long run, you save money on gas.
  • More durability: cars often need to endure harsh conditions. There are only a few examples of freezing winter weather, heavy downpours, and heat waves. An automotive wire harness will still do its work under such conditions. These harnesses are made with sturdy materials that don’t easily crack. 
Close-up view of the car's electrical system

(Close-up view of the car’s electrical system)

How To Pick The Right Wiring Harness for Your Car

The below tips will help you:

  • Inspect the circuit connectors: this is the first and most important. As explained before, standard wiring harnesses have 12 circuits, but others have 18 or 24. You must inspect the circuit connectors to confirm it matches your vehicle type.

Also, check the connection pattern. Does it require crimping or soldering, or both? Having both is best for optimal performance.

  • Check if the harness is expandable: You may have a car that needs a harness with just 12 circuits. Good. What happens if you get a car that needs 18? You can purchase a new harness. Or, you can get an expandable harness that accommodates more circuits from the on-set. An expandable harness is also an advantage as they experience less voltage loss.
  • Check the harness material: You don’t want anything but a durable wiring harness. To ensure this, examine the harness material, especially the wire and connector materials. For the wires, copper is the best option. You can go for copper or brass for the connector but avoid aluminum.
A car mechanic inspecting the wiring harness

(A car mechanic inspecting the wiring harness)


Overall, the wiring harness in a car serves as an important bridge between the vehicle’s electrical system and its multiple electronic components.

It provides power and communications during operation from one component to another.

Without a proper wiring harness, your vehicle’s electrical system will suffer many issues, including power interruptions, decreased efficiency, and even potential fires if not monitored properly. 

It is important to inspect your car’s wiring harness regularly so that you can detect any signs of damage before they become more serious problems.

This way, your harness lasts longer, and you prevent any unforeseen maintenance costs. 

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