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Why do cars need wiring harnesses? What does it do? Mar 30, 2024

Why do cars need wiring harnesses? What does it do?


What is the wiring harness of a car? Cars are large, with an average length of about 4 meters. Still, a car is probably made up of more than 10,000 individual parts that cannot be dismantled, and most of these parts are small.


The wiring harness in the car is responsible for many functions in the car, such as airbags, ABS brakes, signal lights and many important functions in the car. None of these functions would be possible without a harness.


Therefore, we should fully understand the role of automotive wiring harnesses. Next, we will explain the role and importance of automotive wiring harnesses.



What is a car harness?


Automobile wiring harness is the main body of automobile circuit network, and there is no automobile circuit without wiring harness. Wire harness refers to a component that is connected to a circuit after the contact terminal (connector) made of copper is crimped with a wire and cable, and then plasticized to an insulator or an external metal shell.


In simple terms, automotive wiring harnesses assemble cables, connectors, terminals, and wires to transmit electricity in the car.


In the past, cars were purely mechanical and could be driven without electricity. But driving a modern car without electricity would be a miracle.


Therefore, automotive wiring harnesses are a key component of any automotive engine. Without them, the current cannot reach the different electrical parts of the car.


A car's ignition systems, such as the starter, chassis and alternator, require electricity. Without a car harness to transmit them, they can't get that power.


But when it comes to cars, just having a car harness isn't enough. Wires and terminals must also be properly connected to electrical components.


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



(Modern car engine)



Automotive wiring harness circuit


Because car wiring harnesses are connected to different electrical components, they have different connecting circuits.


These circuits have different uses. A conventional standard car circuit has 12.


The circuit includes:

The dashboard light


Signal lamp

Heating and air conditioning


Parking light

Radio broadcast

Brake light


Turn signal lamp




(Automotive wiring harness cables and circuits)


From their names, you can easily understand the function of each circuit.


However, many high-end vehicles have wiring harnesses with more than 12 circuits. Some have 18, some have 24. These additional circuits are important because vehicles are equipped with more electrical components.


If a car has 18 circuits, you will find the following additional circuits:

Electric fuel pump

Electric fan

High stop light

Two power locks

Radio B+ memory


But if the car has 24 circuits, all but 18 are extra circuits:

Dome light

Trunk light

Glove box light


Under hood light

(under hood light)



Components of automotive wiring harnesses


In addition to circuits, automotive wiring harnesses have various components, including:



The connector assembly is exactly what it is named for: it connects the harness wires to different circuits and power supplies. A typical connector has a male end and a female end. The two ends are joined together to transmit current.


However, the type of connector varies, depending on the harness. Their terminals also come in different materials, the best being brass and copper.



(Automotive cables and wires)



Fuse wire


In general, the role of fuses is to protect electrical components in the event of a failure. For example, when the current is too high.


The characteristic of wire harness fuse is that the wire is easily blown at a certain current level. When it fuses, it breaks the circuit.


As a result, it prevents miscellaneous currents from reaching the car's electrical components, thereby protecting them.



(Protective electrical components)



Fuse box


Each circuit in the wire harness has a separate fuse. This means that a failed fuse does not affect all components. A fuse box is like a house where you can assemble different fuses. It's similar to a switchboard.



(Harness behind the dashboard)




Relay components of automotive wiring harnesses are used for high current cycles. It is one of the most important components, drawing power directly from the battery. In contrast, some components get their power from other car system components. Therefore, the relay components can deliver a strong current from a low current.


Electric wire

A harness is an assembly made up of cables or wires. A cable or wire is the component in this view. These are usually copper wires, with different circuit measurement variants.


For example, horn and headlight circuits use 1.5 wire. But the circuits for the dome lights and door lights use 0.5 gauge wires. When purchasing wires for a circuit, it is important to confirm the current value of the circuit.



(Electrical worker checks car wiring)



What are the advantages of car harness?


Having a car harness in the car is better than none at all. Here are some of the benefits they bring:


Less short circuit: For automotive wiring harnesses, the possibility of short circuit is less. Why? Because the harness assembles multiple wires into a well-aligned harness. These bindings are not flexible but not loose.


Quick setup: Installing a wiring harness can take a long time, requiring many wires and circuits to be connected. However, for automotive wiring harnesses, only one unit needs to be connected and all the wires will work. In addition to simplifying setup, you can also avoid incorrect connections.


Better fuel use: Installing car wiring harnesses will ensure that the car optimizes fuel use. You can save money on gas in the long run.


More durable: Cars often need to endure harsh environments. There are very few examples, such as cold winter weather, downpours and heat waves. Under these conditions, car wiring harnesses can still play a role. These harnesses are made of strong materials that are not easily broken.


(Close-up of the car's electrical system)



How to choose the right harness for the car


The following tips will help you:

Check the circuit connectors: This is the first and most important step. As mentioned earlier, standard wiring harnesses have 12 circuits, but others have 18 or 24. The circuit connector must be checked to confirm that it matches your vehicle type.


Also, check the connection pattern. Does it require crimping or welding, or both? A combination of both is optimal performance.


Check that the wiring harness is scalable: The car may only need a wiring harness of 12 circuits. What happens if you have a car that needs 18 circuits? New wiring harnesses can be purchased. Alternatively, an expandable harness can be obtained, which can accommodate more circuits from which to assemble. Extensible harnesses are also an advantage because they have less voltage loss.


Check the wiring harness material: You don't want anything but a durable wiring harness. To ensure this, check the wiring harness material, especially the wire and joint material. For wires, copper is the best choice. You can choose copper or brass as connector terminals, aluminum terminals should be used with caution.


(Auto mechanic checks wiring harness)




In general, the wiring harness in the car is an important bridge between the vehicle's electrical system and its multiple electronic components.


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


Without the right wiring harness, the vehicle's electrical system will face a number of problems, including power outages, reduced efficiency, and even the possibility of fire if not properly monitored.


It's important to check your car's wiring harness regularly so you can spot any signs of damage before more serious problems develop.


This way, your wiring harness lasts longer and prevents any unexpected maintenance costs.

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