HomeTips & GuidesAutomotive Wire Harness Manufacturing Process: A Step-By-Step Guide

Automotive Wire Harness Manufacturing Process: A Step-By-Step Guide

The automotive wire harness manufacturing process often requires outsourcing so that you can focus on building the vehicle. 

And since the harness is a systematic and integrated cable, terminal, and connector arrangement, it requires a planned manufacturing process. Let’s analyze this process below.

Table of Contents


Before getting to the manufacturing process, contract manufacturers need the following information.

  • Bill of materials with part numbers
  • Detailed connector images indicating pin locations
  • A list of wires, wire colors, nets, and connector pin-outs
  • Complete harness test specifications
  • Finished assembly drawing with tolerances, label locations, and assembly instructions
  • Generic specifications like voltage instead of UL codes

The last point enables contract manufacturers to find the most suitable components that are affordable and readily available.

Manufacturing Steps

The manufacturing process always begins with product design.


When designing cable assemblies, consider the vehicle’s electrical requirements and geometry. Use a 3D modeling package and imaging system to streamline this step and prevent or detect faults early on.

An engineering drawing of a harness wiring

An engineering drawing of a harness wiring

Also, consider the cable harness’ performance issues in operation and decide which components you need, their locations, materials, etc.

Design Review

Once your contract manufacturer gets your design specifications, the first step is to inspect the documents for evaluation and to check if everything is as required.

The evaluation process involves checking if the specified components are the best performance-wise, availability-wise, and cost-wise.

The manufacturer should contact you to advise you on better replacements if there are issues.

Materials Preparation

The next step is to analyze the bill of materials and purchase the required parts and materials for manufacturing and testing.

Shelves with wires and connectors for making automotive wiring harnesses

Shelves with wires and connectors for making automotive wiring harnesses

Assembly Documentation

While considering your input requirements, the contract manufacturer will create the assembly documentation for the manufacturing floor. This document must have the assembly steps and test procedures with illustrations and images.

Parts Inspection

Before prototyping, the manufacturer must inspect all the parts purchased for your project for defects. The wires must also meet the American wire gauge or other gauge standards.

And it is the manufacturer’s responsibility to ensure the terminals have the required spacing. All the inspection results go into a digital system to inform the next step. Some of these parts might have to return to the supplier, and the right ones shipped back.

A car wire harness production room

A car wire harness production room


A prototype is a draft version of the idea that lets you bring a project to life to test the features.

Contract manufacturers build these prototypes, then use several inspection, test, and measurement tools to ensure they match the wiring design.

The prototype gets discarded if it fails the tests, measurements, or inspection.

This step helps avoid wastage by ensuring mass production only goes through if the product meets the required performance and quality standards.


This production/assembly process is usually manual because automotive wire harnesses have high customization levels.

Manual manufacturing helps eliminate the geometric and electric issues that can arise when making complex, customized products.

Automotive wiring harness in production

Automotive wiring harness in production

Wire Cutting

Once the prototype is satisfactory, mass production begins by cutting the wires to the required length. A wire-cutting machine handles this process based on markings and measurements.


Manufacturers label the cut wires and lay them out for design matching.


You can only attach naked wires to the terminals or connector housings. So manufacturers strip the insulation of the wire ends to connect them.

But before making the connection, a magnification inspection is necessary to reveal if the core wire or insulation has visible damage.


Inserting naked wire strands into the terminal or connector won’t be neat and can create unwanted connections. So the wire ends must go into a crimping tool, which crimps the wires to the required height.

A wire crimping tool

A wire crimping tool

Loose crimping will leave the wires open and disconnected, while extreme crimping can cause damage. So the crimping must be perfect. Therefore, inspection is necessary after crimping to examine for any defects.


After successful crimping, the wires will insert into the connector housings or terminals effortlessly. But they can come out easily, as well.

So it is vital to seal the joints using solder. And after soldering, manufacturers must inspect the solder joints for any defects.


Inserting and soldering multiple wires into a connector housing or terminal creates the harness assembly. If the cables don’t have joined connectors, they need an outer sheath to wrap the harness together.

An assembly board for wire harnesses

An assembly board for wire harnesses


When the harness is complete, it must undergo electrical safety testing. The wires must have continuity with zero shorting inside or at the terminal/connector ends.

Typical tests include megohm, continuity, pull tests, and visual inspection. If the harness passes the tests, it is ready to use in the car.

Employees checking the quality of automotive wire harnesses on a special stand

Employees check the quality of automotive wire harnesses on a special stand.

How To Enhance The Quality of Wire Harnesses During Manufacturing

Wire insulations will wear faster if exposed to harsh external factors. So consider asking your manufacturer to wrap the wires using either of these materials.

  • Plastic tubes: These protective jackets help protect the wires from extreme weather and other environmental factors, making them ideal for military and industrial vehicles.
  • Gummed tape: This tape secures and protects wire looms in tight spaces. It is essential for seat warmers, audio players, electric window controls, GPS systems, etc.
  • Corrugated tubes: Corrugations strengthen this jacket, resulting in better durability and impact resistance. They might not be necessary in your everyday car, but picture the impacts and explosions military-grade transport cars encounter while in the field.
Wiring harnesses in corrugated tubes

Wiring harnesses in corrugated tubes

Automotive Wire Assembly Benefits

These wire bundles have the following benefits.

Easy installation

Modern cars can have more than four kilometers of wires to power their electrical components. Installing these wires piece by piece can be a tedious and messy affair.

But harnesses integrate the cables, connector housings, and terminals into single devices that are neat and easy to install.

High-Quality Build

Correctly assembled wiring harnesses are tough enough to withstand moisture, vibrations, abrasion, etc.

This quality reduces the chances of experiencing faults like electrical shorts and open circuits. And even if they have a short, they are usually in flame retardant sheaths that stop the flames from spreading.

Car wire harnesses in protective jackets

Car wire harnesses in protective jackets

Other benefits include:

  • Space optimization
  • Enhanced safety
  • Customization
A complex automotive wiring harness

A complex automotive wiring harness

Wrap Up

Manufacturing automotive wire harnesses is a delicate process that requires precision, high-quality components, and multiple inspection cycles. 

After all, you wouldn’t want your car’s electrical systems misbehaving or catching fire as you drive. So the steps explained above are necessary for the manufacturing process. 

We hope this has been an insightful article. Comment below to let us know what you think.

Hi I am Christa, sales manager of Cloom.

I have extensive expertise and experience in wiring harnesses and I believe I can help you.

And we have a very professional technical team who can clearly understand the customer’s needs and give professional suggestions and solutions after receiving the drawings.

If you also have wiring harness needs, please send me the drawing so that we can give you our quote and start our business.

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