The Wire Harness Manufacturing Process: A Guide for Electronics Engineers

Coaching children's recreational league basketball when my kids were growing up was very rewarding—even if it was more like herding cats than playing actual basketball. There is one thing that stands out in my mind, however, and that was when a play worked the way we designed it. We first diagramed the play out for the kids, and then we practiced it until they understood the moves. When it finally came together in a game, it was a beautiful thing to see.

Today, as I work with wire harnesses that are built for electronic devices, I am reminded of those days coaching the kids on how to put the play together. First, the wire harness specifications are drawn up in the same way we would diagram the play. Then, the harness is meticulously laid out, just as we demonstrated to the kids how to execute the play. There's a lot more to the process of course, and thankfully, the wire harnesses usually don't talk back to us. Here are more details of the PCB wiring harness manufacturing process that your contract manufacturer should go through when building your assemblies.

Input: What Your CM Needs for the Wire Harness Manufacturing Process

Contract manufacturers often build both flat ribbon cable assemblies and wire harnesses. To distinguish between the two, a multicore cable assembly is an external connection to devices and will have different environmental considerations, such as their thickness, insulation type, and flexibility. A wire harness, on the other hand, will provide the connectivity between systems in an electromechanical assembly, such as connecting a power supply to a motherboard.

Wire harnesses are laid out and built on a panel that has pegs positioned strategically where the wires will branch out into different directions, or connectors need to be added. This way, the harness is laid out to the exact dimensions that are required. Usually, you specify these dimensions, and contract manufacturers are used to getting a wide range of information to work with. The information can be something as simple as a hand-drawn note, or a series of complex 3D CAD models, as well as everything in between.

However, as with anything that is manufactured, the more detailed documentation and precise specifications you can provide, the fewer problems there will be on the assembly floor. Here is a sampling of the data that will best help your contract manufacturer when building your wire harness:

Detailed connectors images that show pin locations.

Wire lists that specify wire colors, nets, and connector pin-outs.

Bill of materials with part numbers.

Full assembly drawing with label locations, assembly instructions and tolerances.

Finished harness test specifications.

Key Points of the Manufacturing Process to Build Your Wire Harness

With the documentation in hand, you should expect your contract manufacturer to follow a general process in building your wire cable harness assembly:

Design review: First off, your CM will examine your bill of materials and other documentation to make sure that everything they need is in place. They will also evaluate your specified parts to see if those are the best choices due to cost, availability, and performance. If not, they will search for available replacements.

Materials preparation: Once the bill of materials is finalized, the CM will next purchase the components and materials needed for production and test of the harness.

Assembly documentation: At the same time as procurement, the CM will be creating assembly documentation for the manufacturing floor based on your input. This will include detailed assembly steps, images and illustrations, and test procedures. Additionally, the assembly panel will be created with all the necessary pegs set at the specified locations.

Wire harness production: Now, the harness will be built. The assembly technicians will cut the PVC insulated wires to length, and lay it out on the assembly panel according to the build instructions. Connectors will be added, bundles of wires will be tied together, and labels will be attached.

QA: Once completed, the wire harness will go through the testing that has been prepared for it to check continuity. The harness will also be checked for construction and labeling, and tested for fit if the system that it is intended for is on-site.

The building of your wire harness is a pretty straightforward operation, but there are some details you should be aware of to help to speed the assembly through manufacturing.

The Dos and Don'ts of Having Your Wire Harness Built

The component manufacturer usually provides termination recommendations for how the high temperature wires should be attached. Be sure, then, to use those recommendations—such as stripped and bare or stripped and tinned—as that is what the component is built for. The same goes for torque values on fasteners, in which you should also use the manufacturer's recommended values.

You should also provide generic specifications for wires, such as 300V or 600V, instead of a specific UL code. This gives the CM the flexibility to use what works best for the harness requirements that is also readily available and cost the least. Specific UL-coded wire may not be essential for the harness and instead could turn out to be difficult to find or expensive to use.