Automotive wire harness design: Why Design and Planning are important?

Engineers consider practicality, features, aesthetics, and affordability while developing a new product. The wiring harness in a car never changes. Engineers also need to give special attention to the wires’ length, radius, routing, etc. Now, let’s dig into automotive wire harness design.

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What is the automotive wire harness design?

The wire harness provides power and communicates data in a basic manner, whether located behind a car’s glove box or a washer’s rear panel. Whenever an electrical problem arises throughout developing a tech device, an engineer must deal with it.

The difficulty is that each device’s electronic component has a unique design, and the wire harnesses must be constructed in stages. It is necessary to create a unique layout for each electronic component of the product and a systematic procedure for making the associated wire harness. Engineers must also decide on harness components and other useful parameters at this stage.

Quality check on wire harness

Caption: Quality check on wire harness

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What Factors To Consider When Designing A Wire Harness

To bring a wiring harness to market, experts must constantly face and overcome electrical challenges.

Automotive wire harness design: Environmental Considerations

Each harness is unique due to several criteria, the most significant of which is its intended setting. For instance, fires routed close to the exhaust and engine are subjected to tremendous heat. At the same time, other harnesses may be subjected to the elements, including water, dirt, oil, and chemicals.

Likewise, certain wire harnesses are constantly subjected to abrasion from vibration and so require a degree of flexibility. For some uses, picking the right wire is essential. Failures, safety problems, and noncompliance with regulatory criteria like UL, CSA, and CE can all result from wire insulation breaking down due to utilizing the wrong wire.

Automotive wire harness design: Parts Considerations

When working with an outsourcing partner, such as a contract manufacturer, you will likely be required to present a bill of materials along with your drawings. It is important to ensure that your outsourcing partner can easily trace any custom part numbers you include on your drawings back to the original manufacturer and the original component number. Suppose a part doesn’t have to be a certain brand or kind. In that case, it’s beneficial to write “or equivalent” next to it on the package so the manufacturing company can swap it out for something that could improve the harness in terms of quality, speed of delivery, or cost.

Your outsourcer will require access to any internal wiring specifications or standards you have for the wiring manufacture of your equipment. The harness’s termination, labeling, bundling, and other characteristics are often specified in such documents.

IPC/WHMA-A-620 is a useful starting point if you don’t already have a rule and would like to create one. This document contains a set of basic standards that meet the demands of various organizations.

Additional Considerations

Keeping all this in mind can help you select appropriate materials and fine-tune your design.

Lengths and limits

Make sure that you will define the measurements and tolerances. Depending on the original equipment manufacturer’s preference, you can measure the connectors from the front or back.


Some available options include a braided loom, wrap, conduit, split sleeve, and tape. Each serves a unique purpose and comes with its pros and cons. Before deciding which one to use, you should be familiar with its functions.

It’s vital to remember that shielding your wire may not be necessary or even desired in some cases. This is especially true when other factors, such as adaptability, troubleshooting, and serviceability, take precedence.

Positions of splices and splicing

There are various methods for splicing a wire or circuit. It is important to consider the benefits of each type of harness before beginning the design process or sending off your drawings to a wiring harness maker.


Take note of wire colors and any text you want to print or tag on your cables to assist in identifying circuit names. Add them to your drawing for future reference.

Wire Type

Different wires— varying voltage ratings, insulation materials, bare or plated copper, etc.—can be used for various purposes. It is usual to practice, for instance, using UL1015 (MTW) wire in electrical control panels and GXL wiring in automobiles.


Seals, terminals, and connectors come in a wide variety. Many connectors can use terminals and seals designed for various wire gauges, wire insulating thicknesses, and terminal plating. To secure the terminals, ask for the right locks and other equipment.


There is a wide variety of testing procedures that you can perform. The wiring may need high voltage tests for some uses, while a basic continuity test may suffice for others. Think about what might work best for your purpose.

Change Management Plan

It is difficult to strike the ideal balance of details when drawing. It is difficult to understand and maintain overly detailed drawings, leading to questions or an unreliable product. Discuss the best approach to handling markups to drawings, variations, and modifications with your contract manufacturer.

Putting together a complete set of electrical drawings (including schematics, documentation, and layouts) for your project is not always a simple task. It necessitates in-depth familiarity with all the parts and aspects involved, including electrical needs and constraints. Working with a contract manufacturer that focuses on electrical assembly may improve the efficiency and effectiveness of the entire production cycle.

Collection of wires, connectors, terminals

Caption: Collection of wires, connectors, terminals

Best Practices for Wire Harness Design

To work effectively in its physical setting, you need to build a harness following several best practices, including the following:

  • Locate environmental hazards such as electrical noise, temperature extremes, dampness, radiation, etc. Engineers need to consider the effects of their designs on the environment when developing harnesses.
  • Proper routing enables the most effective interaction between wires. While there may be more than one feasible route, you must consider all environmental factors, time and money, complexity, and strain.
  • Cutting wire for the connector and determining the bend radius require precise measurements. The outside wires in a bundle may wind up being significantly longer due to the effect of the bend radius. If this is ignored, the total length will be inadequate. Measure all wires and conductors twice before cutting.
  • The harness has to fit perfectly in its intended place. For example, most companies design small harnesses to fit inside the limited space of cars onboard electrical distribution panels. It’s important to think about the dimensions of the outside protective casings.
  • Mechanical fastening, over-molded connections, plugs, stress reliefs, and ultrasonic welds are common construction details for wire harnesses. When designing, it is essential to consider the types of connectors and how they will fit the cable radius.
Worker setting up a wire harness in the production line

Caption: Worker setting up a wire harness in the production line


Designing and planning a wire harness is important ahead of its manufacture. It might seem like extra work, but it will make the whole process error and problem free. Thus, you must determine all the potential hazards beforehand and work accordingly. Cloom offers wiring harness solutions, so you don’t have to worry about perfection.

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