Auto Wire Harnesses: Everything You Need To Know

About Auto Wire Harnesses, The rise in the quality and range of functionalities in modern vehicles has expanded the need for wire harnesses in the auto industry.

For instance, most modern vehicles have more sophisticated integrated wire harnesses than standard ones.

This blog discusses everything you need to know about auto-wire harnesses. Sounds interesting? Let’s get started!

What are Auto Wiring Harnesses?

A wire harness is an especially bundling way for organizing multiple cables or wires running throughout an automotive (vehicle).

Instead of manually routing and attaching every cable stand strand, cables are trimmed, bundled, and then fastened to the connector or terminal housings to form a single component.

Therefore, it allows for transmitting electrical power and control signals to electrical and electronic devices in a vehicle, ensuring enhanced safety and the basic functionality of an automobile.

It is usually designed based on the dimensional and electrical requirements of the vehicle.

Moreover, it is integrated to connect various parts automobile, such as the chassis, engine, body, dashboard, etc.

Auto wiring harness types

  • Material: Fragmented into aluminum, copper, etc.
  • Vehicle type: Fragmented into commercial vehicles, passenger cars, and two-wheelers.
  • Region: Analyzed Across Europe, North America, LAMEA, and Asia-Pacific.
  • Application: Divided into engine, cabin & dashboard, chassis, HVAC, body & lighting, etc.
  • Voltage: Bifurcated into high and low voltage.
  • Propulsion: Segmented into hybrid, ICE, and electric vehicles.

Benefits of automotive wiring harness

  • Wiring harnesses tie multiple wires into non-flexible bundling, reducing the possibility of electrical circuit shorts and making them safer than faulty wiring.
  • They are vital in increasing the fuel consumption of any automobile.
  • They provide exceptional performance for hybrid cars. For instance, wire harnesses carry electric current even in harsh environments, letting them handle electric loads while resisting high electromagnetic noise and heat.
car mechanic checking fuse.

Car mechanic checking fuse.

How do automotive wiring harnesses work in the car’s electrical system?

A vehicle’s electrical system is a closed circuit featuring a battery and an independent power source.

In addition to the main charging, ignition, and starting circuits, a car has other circuits that power;

  • Heating elements
  • Radio
  • Magnetically operated locks
  • Electric motors
  • Gauges of electrical instruments
  • Sensors
  • Lights

You can open and close these circuits with either relays or switches.

Electric current flows through the car’s metal body (from the battery to the powered car components and back to the battery) along a single cable.

A thick cable connects the vehicle’s body to the battery’s terminal.

The electric current will flow from the positive (+) terminal to the car’s operated component for an earth-return system.

This component is earthed to your car’s body, which is earthed to the battery’s negative (-) terminal.

All the circuits in a vehicle can not be complete without cables and wires.

So, an automotive wiring harness allows information and power to flow through the car’s circuits, like the human body’s central nervous or circulatory system.

Standard Automotive Wiring Harness Circuits

The number of circuits required for your standard automotive wiring harness depends on the electrical components (accessories) you have in your vehicle, as shown in the table below;

Number of vehicle accessoriesAccessories
12-circuit wiring harness12GaugesRadioHazard FlasherWipersTurn SignalsDash LightsStop LightsHornHeat & A/CTaillightsDistributorParking Lights
18-circuit wiring harness18GaugesRadioHazard FlasherWipersTurn SignalsDash LightsStop LightsHornHeat & A/CTaillightsDistributorParking LightsRadio B+ MemoryPower WindowsElectric Fuel PumpPower LocksHigh-Level Stop LightElectric Fan
24-circuit wiring harness24GaugesRadioHazard FlasherWipersTurn SignalsDash LightsStop LightsHornHeat & A/CTaillightsDistributorParking LightsRadio B+ MemoryPower WindowsElectric Fuel PumpPower LocksHigh-Level Stop LightElectric FanGlove Box LightUnder Hood LightDome LightClockTrunk LightLighter

Classification of automotive wiring harness system

The vehicle’s main wiring harness usually takes the instrument panel as the core part.

Therefore, the wiring harness extends before and after the instrumentation panel.

We can classify the automotive wiring harness system into the following;

  • Front wiring harness. It includes the battery wiring harness, air conditioning, front light assembly, engine, and instrumentation.
  • Roof wiring harness. It includes an audio speaker, a roof light, and a door.
  • The rear wiring harness includes the luggage compartment light, license plate light, and tail light assembly.
Circuit diagram

Circuit diagram

Designing An Auto Wire Harness

Several factors influence the wiring harness design. For example, some harnesses, like those that run close to the exhaust or engine, get exposed to extremely high temperatures.

Some may get exposed to water, dirt, oil, or chemicals. What is more, exposure to abrasion, for which the wiring harness has to be flexible.

Based on where you use the harness, you make drawings and listings.

Auto wiring harness parts

You should provide an accurate list of the parts needed for designing your wire harness.

Besides, provide the product’s part number, allowing the partner to precisely substitute the parts to enhance the automotive wiring harness’s cost-effectiveness, performance, and quality.

There are many types of automotive wire harness components, including;


They turn on and off higher amperage circuits, allowing the harness to power several things. They vary according to the amperage requirements.


A fuse prevents power surges from damaging or overloading devices found on the receiving side of the fuse.

Besides, different automotive wire harnesses use different fuse classes.

Furthermore, these components generally vary according to their amperage rating and are usually rated for 32 volts or less.


These are insulators used to keep moisture out of the harness connectors. They can be part of the connector or attached to the terminal.

Strain Relief

Strain relief is normally added to the outside of the conductor. It is usually used to stop the force of pulling wires in the connector that can enable the terminal to pull out of the connector, which can cause a bad connection.

Also, you can add them at an extreme bend radius which may put undue force on the terminal and wire inside the connector.


Cable ties keep the wires inside the harness attached, forming a stream of wires in a particular direction.

It also attaches to a structure or device at fixed points, which minimizes movements.


Locks are normally attached to the connector to stop the terminal attached to the wire from pulling out of the connector.

It also ensures full insertion o the terminal into the connector.

Automotive wire harness marking

These are symbols of letters and numbers marked on the wire object connection. You can identify circuit names using labeling language and wire colors.

The operator can correctly see the symbols connected to the corresponding electrical devices and wires.

Automotive wire harness Covers/wrapping

The surface of the wire harness is normally wrapped in multiple ways depending on the parts of its use.

Every material has a distinct purpose and unique benefits and weaknesses. Therefore, you should understand the purposes while choosing a material to use as a cover.

  • Engine wire harnesses operate in harsh environments. Therefore, you can wrap them using waterproof, high mechanical strength, and flame-retardant threaded pipe.
  • The front cabin works in a relatively poor environment. Therefore, you can wrap most branches using threaded pipes with great flame retardancy.
  • The headliner line, instrument line, and door line workspace are small. So, you can use a tape full wrap.

Automotive wire harness connector

Wire harness connectors disconnect or connect prefabricated components or parts to the wiring harness.

They are available in multiple colors, sizes, and varieties to connect different types of harness wires.

While automotive wire harness connectors are usually plastic, you can design them from multiple elements, including ceramic and metal.

Automotive electrical wire types

Automotive electrical wire carries a signal or current that powers a device. The capacity of the wire must meet or exceed the bandwidth or voltage it should transmit.

There are many types of wires, including copper-plated or bare and insulating material. And each type of wire is ideal for a specific application.

Motor Wire: It has finer strands of copper wire. Therefore, they can endure higher temperatures of up to 221°F and voltages of up to 600 volts without burning up.

Battery Cable: A cable connects the battery to the car’s electrical system and the ground. It is usually a thicker but smaller-gauge wire.

Speaker Wire: A speaker wire allows the audio signal to flow from the stereo receiver or head unit to the speakers. These types of wires are designed for low-voltage applications.

You must install the negative and positive terminals of the wire in the correct locations. Your speakers will not sound correct if you fail to do this.

n the correct locations. Your speakers will not sound correct if you fail to do this.

Wires with connectors marked with different colors

Wires with connectors marked with different colors

Additional Information to Outline

Wire Size/Gauge: the gauge you require depends on the wire length between the power source and the circuit and the current draw of the circuit.

Overload protection required: Overloading a wire is risky for your customers and staff.

For instance, a wire with an incorrect current rating can short out, damaging essential systems, starting fires in extreme cases, and stall equipment in dangerous locations.

Therefore, you should know your amperage and (always ensure that the wire you purchase can take the load.

Besides, confirm the type of circuit breakers, fuses, relays, and other overload protection required for your wiring project.

Wire Materials: Copper is more flexible, conductive, and less corrosion-prone than aluminum.

However, it is vulnerable to price fluctuation and weighs more. On the other hand, aluminum is cheaper and lighter.

However, it is less durable and prone to developing electrical resistance or corroding. Most automobile applications use wires made of copper.

Wire core: Solid wire is only suited for industrial and home uses. Automotive wiring must be flexible, which makes stranded wire core ideal for automotive wiring harnesses.

Automotive wire Insulation:

Made by heating PVC and forcing it out through a die on the stranding. The main PVC automotive wire insulation types are GPT, HDT, and TWP.

Cross-linked wire insulation: Created by extruding polyethylene via a tube under pressure and heat. They can withstand relatively higher temperatures than PVC wire insulation. The common types are GXT, SXT, and TXT.

Wire Coloring, Striping, and Printing: Colors are often used to trace and identify a wire to a corresponding electrical circuit.

For example, in tractor-trailers, the yellow color scheme signifies right light, while brown wire signifies left light.

You can also expand your color scheme by adding a color stripe. For instance, you can order printed wording that shows the exact use of the wire.

The majority of suppliers will perform customer printing and striping.

  • Length and tolerance: You should know the wire sizes, dimensions, and lengths. Also, consider tolerance according to the shape and length required.
  • Splicing and splice location: Splicing a wire is one of the critical steps in the wire harness design process. And there are many splicing techniques. Therefore, review the splicing technique you want to use before deciding on the wire harness design.
  • Soldered or Solderless:  Soldered connection is prone to errors and is time-consuming. It is obsolete for most automotive wire harnesses today due to the availability of a wide range of solderless connectors. Besides, most connector and wire manufacturers discourage soldering because of the difficulty of ensuring quality control during the harness process. These connections have become the easiest and fastest method to terminate wires. They entail using commonly available wire connectors like ring terminals, spade terminals, and quick disconnects.

Caption: The Basic Formula for Amps, Gauge, and Wire Length

Change Management Plan

Achieving an exact balance of details on a drawing is almost impossible.

For instance, too many drawings and details can be cluttered, prone to inconsistencies/errors, hard to read, and difficult to maintain.

On the other hand, few details can lead to inconsistent products and many questions.

Therefore, you should work with your manufacturing partner to change your management plan and determine how best you can handle revisions, deviations, and drawings.

Production of Automotive Wire Harnesses

Manufacturing in the current global economy involves advanced smart technologies that enhance efficient production.

For instance, a combination of advanced input and output technologies, computer modeling, automation and control techniques, simulation, and CAD design.

However, this is not the case with the wire harness manufacturing process.

Although modern systems and computer technology are utilized in the pre-assembly and design stages, the actual wire harness production needs more than what automated manufacturing can offer.

It needs a personal touch.

Processes Automated

The ends of individual wires that need stripping and cutting can be achieved using specialized cutting machines.

Besides, you can solder the wire ends via automation.

After completing the assembly, the wire harness is tested for electrical functionality, which is partially automated and utilized using a test board meant for the wire harness.

Processes Manually

After the schematic design to assemble the automotive wire harness, a manufacturing process is done manually. 

Running cables or wires through conduits and sleeves or installing terminated wires in different lengths must be done manually.

Specified wires, when multiple wires are going into one terminal, need multiple crimps done by hand.

Moreover, different components should be harnessed or bound by hand with cable ties, clamps, and tape.

The Manufacturing of Automotive Wire Harnesses.

Automotive wire harnesses are manufactured in three phases;


The cutting area’s wire harness process is highly automated. For instance, CST (Cut, Strip, and Terminate) machine does the following;

  • Cut (C): Cut the wire to specific lengths
  • Strip (S): Strip off the insulation
  • Terminate (S): Apply terminals and seals

More complex machines also perform extra process steps like twisting wires. All the wires produced in this method are grouped into bundles.

They are then made available for the next production step.

In the CST machine, the wires are sometimes tiny in diameter, and the wire harness production rates are normally very high.

Although the CST machine mainly ensures quality and precision, MES contributes by directly transferring the control data, like crimp data, to all the connected machines.

Moreover, to set up traceability, a unique ID is assigned to each produced wire bundle and continuously managed throughout its history.


The next phase of wire harness production is highly manual. In the initial pre-assembly phase, you need to assemble the wire bundles produced in the cutting area into simple kits using procedures like;

  • Twisting,
  • Ultrasonic welding,
  • Crimping.

Final Assembly

The automotive wire harnesses are assembled on the wire harness boards in the final assembly phase.

These boards are generally mounted on a moving assembly line.

Since the wiring harness is normally produced to be customer-specific, the process steps can vary from wire one wire harness to another.

So, there are high chances of making errors, which is an extra challenge for quality assurance.

However, the MSE software can offer a high-quality level in these auto cable harness manual processes.

Repair the Automotive wiring harness.

It would be best if you remembered a few habits and instincts while repairing automotive wire harnesses.

Safety First,

Whenever you add new wiring or perform wire repairs, disconnect the positive and negative terminals of the battery.

Resultantly, there is no power in the system, ensuring you do not get shocked and preventing potential circuit damage or shorting damage.

Know the circuit

Computer-controlled injected cars have a lot of circuits carrying low-voltage signals.

For instance, repairing these wires with too much solder adds enough resistance, which can cause computer miscalculations and signal errors.

Therefore, knowing the circuit while repairing an automotive wiring harness will help you avoid the check engine light or running problems.

Ensure backshells and connectors are in good condition.

If these parts have sustained damage or are corrupted, you need to replace them before installing your electrical wiring harness.

Besides, ensure you get the right size when crimp-style connectors are needed.

If they are too small, you may need to strip a few wire strands to get them to fit, leaving a circuit too weak to carry the load.

Conversely, the crimp will not be solid if the connector sizes are too big.

Break wires out of the harness carefully.

If an electrical wire already in a harness must be repaired or replaced, the removal should be done carefully to avoid damaging adjacent connectors or wires. For instance, you must bend the wires as little as possible, particularly near the connector.

Secure wires with heat shrink tubing.

After repairing the wires, they should be securely wrapped in the correct heat shrink tubing. Therefore, you should select a heat shrink tubing that is large enough to slip over the harness wire you need to wrap. In addition, it should be able to shrink down enough to fit snugly on the wire bundle.

When repairing several wires, you should use the heat shrink tubing on the individual repairs. However, you should follow up with a larger heat shrink tubing that bundles all the strands together, giving a cleaner result.

Use Electrical Tape Properly

Black electrical tape is useful and often used in vehicle wiring to bundling wires. However, you should never use it to protect a new repair, as temperature and moisture variations will make it loosen and unwrap.

Choose Cloom as Your auto wire harness manufacturer for Custom Automotive Wiring Harnesses. 

However, you must replace the entire wiring harness if the damage is extremely extensive, such as melted wires.

Also, you should replace more sensitive systems, like airbags, rather than repairing them.

The cost varies widely depending on the locations and sizes of wire harnesses. Contact Cloom for help.

Automotive Manufacturing Design Resources

Our team of experienced and knowledgeable application engineers offers design consultations, as required, to refine your wire harness design for more cost-effective, faster, and better production.

Furthermore, they work with you to develop an optimized solution that delivers the performance and quality your application requires.

Manufacturers & Suppliers

Cloom works with some of the industry’s top manufacturers to maintain a large in-stock inventory of high-quality interconnect materials and products.

These partnerships help us ensure that our customers receive the best automotive wiring harness and cable assembly solutions.

For instance, Cloom works with the following manufacturers;

  • TE Connectivity (formerly Tyco),
  • Molex,
  • Bosch,
  • Furukawa,
  • ITT Cannon,
  • Delphi,
  • Deutsch,
  • Sumitomo.

Quality & Performance Testing.

Our automotive wiring harnesses are ISO-compliant and meet IPC/WHMA-A-620 quality standards.

Cloom is also CSA and UL certified; our production facility is RoHS compliant.

Moreover, we recycle all scrap and waste materials to maintain green manufacturing processes.


The automotive wiring harness is subject to much damage throughout their lifespans, which can be overwhelming.

Fortunately, at Cloom, we make custom automotive wire harnesses that you can use in your car.

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