Wire Harness Assemblies: Ultimate Guide

Wire harnesses are a small but mighty component with many benefits for manufacturing. In this post, we'll deep dive into the basics of wire harnesses.

What is a Wire Harness? 

A wire harness is an arrangement of wires or cables sheathed together in an insulated material--typically either a thermoplastic or thermoset material--that protects the wires from environmental conditions that could damage the wires.  

A wire harness is a ready-to-install component that simplifies connections to larger components and helps keep electrical wires organized and protected from damage. They can range from simple to quite complex--with many wires, components, and terminations.  

Example of a wire harness

Wire Harness Applications

Wire harnesses are used in a wide variety of applications, including electronics manufacturing, automotive manufacturing, the manufacturing of industrial and construction machinery, and the production of household appliances like washers, dryers, and refrigerators.  

What's the Difference Between Wire Harnesses and Cable Assemblies?

Wire harnesses are often confused with cable assemblies. While the two are similar and the terms are often used interchangeably; however, the primary difference is the environment they are used in. Cable assemblies are generally much more robust and heavy-duty compared to wire harnesses because they are used in more difficult environments and more extreme conditions. While wire harness assemblies do offer a degree of protection, they are not intended for the demanding environments where they would be frequently exposed to heat and moisture. 

Benefits of Wire Harness Assemblies 

Fast installation enables greater production efficiency

A wire harness combines multiple wires and cables together into a single unit, enabling fast and simple “drop-in” installation. This also means that an OEM only needs to install one component, saving significant time compared to running each wire individually. This means faster and more efficient production of goods--from electronics to cars to household appliances and more. 

Secure, protected wiring ensures quality in manufacturing 

A wire harness also protects the entire assembly from wear and damage due to friction and vibration. Wrapping wires and cables in a flame-retardant sheathing material also reduces the risk of electrical fires. This not only protects the wires themselves, but it also helps ensure the quality, reliability, and longevity of the end product.  

Space savings

Bundling wires together also keeps electrical systems organized and optimizes the use of space, reducing space requirements for electrical wiring and allowing for more flexibility in product design.  

How are Wire Harnesses Designed and Assembled? 

A wire harness assembly is typically custom built to meet the unique requirements of your design, particularly the specific electrical and space requirements where the wire harness assembly will be installed. At ISC, our in-house tooling group will meet with you to understand the demands of the application, determine the specifics of the assembly, and design a custom solution.  

We use state-of-the-art drafting tools to design your assembly and bring it to life on screen before we go to production. Then, we collaborate with you to deliver a complete, turnkey solution that meets your exact requirements--built for both cost and design for manufacturability.  

Once the design meets the necessary standards, the wire harness assembly process can begin. This typically includes installing wires, cables, and/or subassemblies on an assembly board, routing the wires through sheathing, and crimping terminals onto the wires. This is a delicate process and one that is still mostly done manually, as it is difficult to fully automate. 

What Causes a Wiring Harness to go Bad? 

Wiring harnesses that go bad can be a nightmare scenario depending on the application. When wiring harnesses fail, they can cause a short or open circuit, which is frustrating at best and, at worst, can be devastating if the wiring harness is delivering power to a mission-critical application.  

There are a variety of reasons a wiring harness can fail, but it mostly comes down to the original design. For example, common causes of wire harness failures include incorrect wire preparation, poor harness layout, defects introduced in the crimping or soldering process, and incorrect or missing hardware.  

To avoid potentially catastrophic failures, it’s important to get the design and manufacturing of wire harness assemblies right. Partnering with a contract manufacturer that adheres to the highest quality standards can make all the difference, which leads us to perhaps the most important question: 

How to Ensure Quality for Wire Harness Assemblies? 

Once assembled, wire harnesses are tested to ensure that quality standards are met. To ensure the highest quality wire harness assemblies, look for a local contract manufacturer with a clearly articulated quality policy that is in line with the framework laid down within ISO/AS 9100:2015/16 standards.  

For example, at ISC, our wire harness test procedures include dimensional gauging, functional testing, press force monitoring, failure probing, continuity testing, and more. In addition, our quality system is monitored, measured, evaluated, and enhanced regularly to ensure our solutions meet or exceed customer expectations. This ensures the highest performance, reliable solutions for our customers.  

Wire Harness Assemblies for Military and Aerospace  

Wiring harness assembly requirements vary by industry and application. For military and aerospace, there are special considerations that must be taken into account to ensure that wiring harnesses can meet--or exceed--the demands of the application.  

Special Requirements for Military Use Cases  

Defense contracts necessitate compliance with strict quality control and traceability standards, as required by various government agencies. The following are several important government agencies and manufacturing standards that are applicable to military wire harness assemblies: 

  • NEMA (National Electrical Manufacturers Association) defines and publishes standards for all electrical equipment in the US.  
  • QPL (Qualified Products List) is a list of products that comply with government regulations.  
  • WHMA (Wire Harness Manufacturers Association) issued IPC/WHMA-A-620 Class III, the single industry-wide standard for manufacturing, using, and installing cable and wire harness assemblies.  
  • MIL-STD-454 is the industry standard for electronic equipment for military use cases.  

In addition to following all relevant manufacturing standards, each use case presents its own unique challenges. As an example, for military aircraft, weight and space constraints are especially important to avoid impact on aircraft performance. High vibrations and frequent altitude changes must also be taken into consideration.  

ISC’s Military Industry Capabilities 

At ISC, our wire harness assemblies are custom-built, designed, and rigorously tested to the highest quality standards. Our wire harness assemblies support a wide range of critical military and defense applications, including use in: 

  • Unmanned vehicles and drones
  • Marine systems
  • Military aircraft
  • EMI-sensitive equipment
  • Military ground equipment
  • Tactical field command platforms
  • and much more

ISC has been providing assembly services to the military industry for over 25 years. Beyond wire harness assemblies, these services include land, air & sea-based detection, weapons, defensive systems for aircraft assemblies, electro-mechanical box builds, complex wiring and connector systems, and electronic sub-assemblies for military aircraft and defense systems.  


With over 50 years of cable and wire harness assembly experience and 25 years of serving the military and defense industries, ISC is equipped to tackle any problem our clients face while providing top-quality solutions at a fair price. No matter the level of complexity a wire harness assembly requires, we have automated tooling, assembly aides, and engineering support for quality and efficient manufacturing. Our processes help build and certify assemblies and components to UL, ITAR, and RoHS compliance. 

Contact us to learn more. 

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