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HomeTips & GuidesAutomotive Wire Harness Design: Steps, Importance, and Factors to Consider

Automotive Wire Harness Design: Steps, Importance, and Factors to Consider

Automotive wire harness design involves creating and developing the cable assembly for a vehicle’s electrical system. 

Modern cars have complex wiring systems, so the design process must involve a wiring diagram to capture the car’s electrical components to connect and the wire lengths. 

Let’s look at the automotive wire harness design process, its significance, and factors to consider.

Table of Contents

Automotive Wire Harness Design Process

The design process involves these six steps.

Gather the Requirements

Get the information about the electrical components to connect in the vehicle and their locations, constraints, etc., from the vehicle manufacturer. Gather as much information as you can.

Create a Schematic Diagram

Build a schematic diagram using specialized wiring software to indicate the connections between the electrical components.

These electrical connections are the wiring harnesses, and the schematic might go through several revision iterations based on the testing feedback for fine-tuning.

A schematic diagram

A schematic diagram

Choose Materials and Components

Using the schematic diagram as a guide, select the appropriate connectors, wires, sheaths, grommets, etc., needed for the wiring harness.

And consider the internal and external factors, such as wire gauge (power load), vibrations, heat, moisture, etc., when choosing these materials and components.

Create a Physical Layout (Wiring Diagram)

A wiring diagram is different from a schematic diagram because it details the physical location of components, plus their dimensions and interconnections (physical layout).

Schematics show the function and plan of the electrical circuit, usually to communicate the circuit operations to other engineers for fine-tuning. They are more logical than physical.

When creating this physical layout, consider factors like space constraints, maintenance, installation accessibility, and repairs.

A wiring diagram

A wiring diagram

Wire Harness Manufacturing

Build the harness to match the specifications in the schematic diagram. Also, adhere to the physical layout when cutting wires to ensure the wire harnesses meet the required wire lengths. Check the wire color, as well.

Wire harness assembly (installing connectors and terminals)

Testing (Quality Control)

Once you complete the wire harness assembly process, test the bundles to ensure they meet the required durability and performance standards.

The harness should not get installed in the vehicle with manufacturer defects.

Factors To Consider When Designing an Automotive Wire Harness

Consider these 12 factors.

Wire Harness Purpose

The primary function of a wire harness is to transmit power and communication signals between devices. But ask yourself, what is its purpose? If for the head unit, the cables can be the regular type.

However, if the wire harness assembly is for connecting components in the engine bay, such as the electrical control unit, it should be able to withstand heavy vibrations.

Other wires might need EMI resistance properties, so match the harness to its purpose.

Wire Selection

Specifications like wire gauge, length, color, and mechanical properties should match the harness’s applications. 

And wire gauge usually goes hand-in-hand with length. A longer wire experiences more electrical resistance, so it has to be thicker to minimize the current and voltage drop.

Wire harnesses must also feature color codes to enable correct wire identification during repairs in the future.

Multicolored wire harnesses

Multicolored wire harnesses

Lastly, the assembly of wires should withstand the mechanical stresses of bending, flexing, and twisting without snapping.

Environmental Factors

Some harnesses might get exposed to high temperatures due to being close to the exhaust or engine. Others might face high water pressure, chemicals like grease, or other factors that can break/burn the insulation.

So pick a wire with the respective insulation that can withstand these conditions for maximum durability.


Wire harness connectors link and protect the cable joints from environmental conditions.

Butt connectors are some of the best for joining individual wires, but you should pick the connector based on the required electrical and mechanical properties.

Also, consider factors like wire gauge, circuit density, ease of joining, and space availability when picking a connector type.

And remember to consider the board-to-board, wire-to-board, and wire-to-wire terminations, as well.

Standardize these components to make parts sourcing easier and enable quick reviews of parts price details.

Wire harnesses with plastic housing connectors

Wire harnesses with plastic housing connectors


Wire routing is vital when drawing the physical layout because it determines accessibility. So optimum positioning is crucial to create an easy-to-install, maintain, and replace wiring harness.

And when routing, consider factors like EMI that can mess with signal quality. Design the harnesses to pass through areas that experience little to no interference.

The wires themselves can also cause EMI. So separate them based on their signal type, voltage, or function as they head to their respective electrical system points or end devices.

Strain Relief

A wire harness assembly exposed to pulling, vibrations, and other forms of mechanical stress can snap or become loose if it does not have strain relief. So implement strain relief features in your design after identifying the sources of this mechanical stress.

For instance, you can use flexible wires, lengthen the harness, or, depending on the situation, install cable clamps, grommets, or cable ties. And you should install these components on the weak points, such as where the individual wires exit the harness.

A car door wiring harness grommet

A car door wiring harness grommet

Outer Jacket

Each wire has color-coded insulation, but this protection is insufficient for safeguarding the cables.

So include an additional insulation layer to protect the wires from abrasion and environmental conditions like heat, moisture, and chemicals.

But first, consider the installation environment before picking the material to use for the outer jacket.

For instance, a fuel pump harness should have a chemical-resistant sheath for protection against gas in case of a leakage.

An insulated wiring harness

An insulated wiring harness

Wiring Harness Diagram Software

Developing wiring designs using advanced CAD software has these benefits.

Quick Issue Identification and Resolving

CAD software can enhance your wiring harness’s designs by ensuring they are precise and meet manufacturing standards.

Also, these applications make it easy to spot issues like wire length limitations, wire-to-wire interference, and voltage drops to ensure you adhere to industry standards.

Quickens the Design Process

Automated error detection and reduction hastens the design process while reducing reworks. Also, you can label the physical layout diagram to indicate splices and connectors.


Ensure you send your parts list to your manufacturer when designing the harness to confirm component availability.

If unavailable, this partner should advise you accordingly, giving you other options or better alternatives.


Always design the harness while having the quality control process in mind to avoid downtimes during testing.

For instance, consider the equipment at your disposal for testing things like mechanical strength and electrical integrity.


The wire harness will go to cars all over the globe, so create design documentation that includes the connector information, schematic design, physical layout, etc. This document will simplify troubleshooting and repairs.


Lastly, comply with all regulations and standards when designing this electrical hardware.

Importance of the Automotive Wire Harness Design Process

The wire harness design process is significant because it provides these benefits.


Designing before manufacturing highlights faults like mechanical stress that can snap wires and cause shorting or fires. So the process is critical because it ensures the final product is as close to perfect as possible.


Without product design, the harness can experience cuts, stretching, malfunctions, or signal interference that cause car electrical parts to misbehave. You can avoid these reliability issues by investing in an extensive design process.

Engine wiring is protected using corrugated tubes

Engine wiring is protected using corrugated tubes


A well-designed automotive wire harness is more adaptable because it can accommodate more changes or system upgrades when modifying the vehicle.

Cost Effectiveness

In addition to making the wiring flexible, a well-designed harness is easier to install. The optimized design can also have fewer components or connectors, making it cheaper.

Wrap Up

As you can see, the automotive wire harness design process is vital before manufacturing because it enables optimization. 

Additionally, it ensures safety, flexibility, reliability, and compliance with various standards. So it is essential for wire harness production, and we’ve detailed the steps you need to take. 

Contact us if you need further guidance in this design process. We’ll be in touch to help.

I am Lillian Yang, having been a sales manager for over 10 years.

I have received many positive reviews from customers. They have praised our excellent service, on-time delivery, and high-quality cable assemblies.

For your projects, please provide cable assembly files/images/smples, etc., so that I can send you a quotation within 24 hours.

Contact me now and let’s get started on building your wire harnesses!

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