4 Design Considerations For Custom Automotive Wiring Harnesses

Designing an automotive wiring harness presents a unique set of challenges for any type and size of vehicle.

A secondary custom wiring harness may be required for installing a GPS tracking system, two way communications radio or even a specialised console interface.

Regardless of the application, the harness needs to be precisely built in order to withstand exposure to specific conditions within a vehicle, such as engine vibration.

While a harness design may look good on the drawing board, it might not be practical or even feasible when it comes to actually installing it inside a vehicle.

In this article, the experts at QCC Custom Cables explain 4 key considerations that need to be taken into account when designing a custom made automotive wiring harness.

Using The Right Connectors

All vehicles have existing wiring harnesses using specific types of connectors. When designing a secondary wiring harness, the connectors used have to meet the same specs from the vehicle manufacturer.

If there are differences in the quality or type of connectors used, there will be weak links in the wiring.

The same type of connectors also need to be used so that an automotive engineer can easily understand how the harness works and how it impacts on other wiring.

Another point to note is the design of primary wiring harnesses can differ between models of the same type of vehicle.

This makes it very important to thoroughly check that the right connectors are used in a new custom made automotive wiring harness.

RF (Radio Frequency) Interference

Using the correct type of shielding is very important for a custom made automotive wiring harness. Shielding can be composed of braided strands of copper or a layer of conducting polymer, covered with a plastic jacket.

Inadequate sheathing can cause the wiring to act as an unintended aerial, picking up and emitting Radio Frequencies. In other cases, the RF can interfere with other electronic equipment in the vehicle and potentially cause malfunction.

With continued advancements in vehicle electronics, such as parking sensors and voice activated controls, it has become more necessary than ever to ensure effective RF interference shielding is used.

RF shielding needs to be a high priority in the early design phase to avoid working retroactively to create a viable solution. Determining the correct type of shielding often requires an expert understanding of custom wiring harnesses and the potential impact the cables have on the other electronics in the vehicle.


A secondary wiring harness can easily add a significant amount of weight to a vehicle.

Complex harnesses which power multiple devices can weigh as much as 50 kg or more. This weight can have an impact on the licenced payload for trucks and buses especially.

The issue of weight needs to be thought about carefully in the design phase. Weight saving measures can be incorporated into the design of the harness, such as using certain types of materials and minimising cable lengths where possible.

Routing Of The Harness

A major determinant in the design of a custom made automotive wiring harness is how the harness will be routed through the vehicle.

Size and ease of access needs to be thoroughly considered as these factors will directly influence the size and type of cables which can be used.

The harness may need to be routed through the chassis or between the cabin and engine bay. Aerials, external lights and sensors all need to be considered as well.

The conditions the harness will be exposed to as a result of how it is routed must be taken into account. A harness which runs through an engine bay will require sufficient protection from high vibration levels as well as high temperatures. Dust and water proofing may also be required.

Failure to ensure sufficient protection against these elements will result in the wiring harness becoming frayed and worn, ultimately leading to failure.

To Wrap Things Up

So as we’ve discovered, there are many unique design considerations that need to be factored in to a custom made automotive wiring harness.

Understanding all of these unique considerations and designing accordingly requires the experience of an expert.

If you have a vehicle project that requires a custom wiring harness, call the team at QCC Custom Cables.

We have the right expertise to deliver a workable solution for you, in full and on time.

For more information and advice, simply click here to get in touch.