Introduction to Prototype Wire Harnesses in Vehicle Development

Creating and testing a wire harness prototype is a critical step in vehicle development. The wire harness is the vehicle’s circulatory system, delivering power and signals to all electrical components. When wire harness issues arise, they can disrupt vehicle functionality and compromise safety. Testing a wire harness prototype before installation can help identify defects and ensure the harness aligns with specifications. By thoroughly testing the prototype, teams avoid costly reworks and provide reliable, high-quality performance in the final vehicle.

The Challenge of Detecting Wire Harness Defects in Installed Systems

Wire harness defects are often challenging to detect once fully installed in the vehicle. When installed, the harness is embedded within panels, components, and assemblies, making it difficult to access, inspect, or repair. Common issues include incorrect wire routing, loose connections, errant wire interconnects, missing interconnects, damaged insulation, or mislabeled connectors—any of which can disrupt vehicle operation. Detecting these issues after installation can be costly and time-consuming, often requiring the disassembly of parts and even retesting of entire vehicle systems.

Harness Development and Time

This problem is further exacerbated when there is a temporal gap between the completion of the prototype design drawings and the availability of the prototype wire harness. If the prototyping wire harness is being built when many change requests are being submitted, it can be difficult to trace which change requests are in which prototype wire harness. This is but one of the reasons why we should have a record of the wire harness changes submitted to the wire harness supplier, along with a notation of what is in the wire harness build.

From experience, there are often changes to the vehicle that will have implications on the wire harness.  These changes may be sent to the wire harness prototyping entity in-house; perhaps we can create the wire harness relatively quickly. However, large and complex wire harnesses, such as cab wire harnesses for commercial vehicles, can take many hours to produce.  If we send the wire harness out to the production supplier to fabricate, from experience, we can expect a small number of parts to take more than 8 weeks, including shipping time (and it can be longer).  This length of time between ordering the prototype and the delivery of the prototype makes these interim changes more difficult to manage.  If we send change requests to the supplier, we need a way to understand what is in the prototype.

The Value of Testing the Wire Harness Prototype Before Installation

Testing the wire harness prototype early in development helps to catch and correct issues before they reach the assembly line. Through rigorous prototype testing, teams can evaluate electrical connectivity, verify continuity, and confirm that each wire is correctly routed and secured. Testing before installation saves significant time and costs compared to addressing defects once the harness is integrated into the vehicle.

Wire harness testing before installation also allows for simulated testing of real-world electrical conditions. By measuring current load, resistance, and voltage drop across the harness, engineers can ensure that the prototype meets or exceeds the performance specifications defined in the drawings. Early testing provides a comprehensive understanding of the wire harness’s performance, preventing potential in-vehicle issues.

Comparing Wire Harness Prototype to Engineering Drawings

Comparing the wire harness prototype to the engineering drawings is essential to ensure that the prototype conforms to design specifications. Engineering drawings detail the precise routing, pin configurations, wire gauges, and connector types, acting as a blueprint for the prototype.

Steps for Comparison

1. Visual Inspection: Compare each wire in the prototype against the drawing.  Verify that it matches the routing, labeling, and color coding specified in the design.
2. Connector and Pin Mapping: Ensure each connector is correctly pinned and all wiring paths align with the designated circuits.
3. Measurement Verification: Check wire lengths and configurations to confirm they match the drawing’s dimensions. Avoid unnecessary tension or slack that could impact performance.
4. Continuity and Insulation Tests: Measure continuity for all connections and confirm that each wire is adequately insulated to avoid shorts or cross-connections.

And Automation

We prefer automating the testing of the interconnections of the wire harness; performing a manual continuity test is laborious, and errors are easy to make.  With automation, our wire harness design documentation is exported to a specific format and imported into the test fixture.  The most challenging part is building an interface harness to the test fixture. The upside, though, is we can quickly test every prototype – in seconds, hundreds of interconnects are tested for:

• Continuity
• Discontinuity
• Cross continuity not connected to the design
• Intermittent continuity

We can test many wire harnesses in a fraction of the time it takes to test one. This can be helpful if we are building several prototype vehicles and iterations. The intermittent continuity is also helpful when we have a difficult-to-identify issue in the wire harness. If you have troubleshot a wire harness, you know what I am writing about.

By thoroughly comparing the wire harness prototype to the drawings and automating them where possible, teams can ensure that the harness will meet performance requirements and integrate seamlessly with the vehicle’s systems.

Methods for Testing Wire Harness Prototypes

Testing the wire harness prototype involves a combination of automated testing tools and manual inspection. Below are standard methods:

1. Automated Continuity and Shorts Testing

Continuity testing ensures that electrical connections are intact, while shorts testing confirms no unintended connections between wires. Automated testing tools quickly identify any breaks in continuity or short circuits, reducing the chance of undetected defects.

2. Load and Current Testing

Load testing simulates real-world electrical conditions to assess the harness’s ability to handle expected current loads. This testing verifies that the prototype can manage power delivery without overheating or excessive voltage drop.

3. High-Pot Testing for Insulation Integrity

High-potential testing checks the insulation’s ability to withstand high voltages without breaking down. By applying high voltages to the harness, this test ensures that each wire is insulated correctly. This is critical for preventing shorts that could affect vehicle electronics.

4. Pin-to-Pin Resistance Measurement

Pin-to-pin resistance testing involves measuring the resistance between two points in the harness, ensuring that each wire meets the resistance specifications indicated in the engineering drawings. Higher resistance levels could signal poor connections or undersized wiring.

Enhancing Vehicle Quality with Rigorous Wire Harness Prototype Testing

Creating and testing a wire harness prototype before vehicle installation is essential for preventing costly errors and ensuring reliable performance. By identifying and addressing defects early, vehicle developers can enhance product quality, minimize downtime, and improve customer satisfaction. Through rigorous testing and careful comparison with engineering drawings, teams can create a dependable wire harness that aligns with vehicle specifications, reducing the risk of performance issues post-installation.

Wire harness prototype testing is an invaluable step in vehicle development, setting the foundation for a safe, efficient, and reliable electrical system.