Wire Harness Testing: Methods, Tools, and Best Practices

Live electrical wires carry currents. While some damage may be minor and manageable, faulty wiring has the potential to cause significant system failures, resulting in irreparable harm to equipment, finished products, and even surrounding property. As such, wire harness testing is crucial to ensure safety and reliability.

What’s the Purpose of Wire Harness Testing?

The primary purpose of wire harness testing is to detect defects that could compromise the performance and safety of electrical systems.

These tests also ensure that each harness component meets design specifications and functions as intended. 

Common defects that wire harness testing can identify include:

• Incorrect or mis-wiring – Errors in wiring layouts that can lead to malfunctions or failures.
• Loose connections – Poorly secured terminals or connectors that may result in intermittent connections or system failure.
• Incorrect wire gauge – Using wires of the wrong size can lead to overheating or insufficient power delivery.
• Failed or incorrect components – Defective or mismatched parts that can disrupt circuit operation.
• Bad joints and crimps – Weak or faulty connections compromise electrical continuity and reliability.

The 3 Pillars of Wire Harness Testing

Wire harness testing focuses on three critical aspects: mechanical, electrical, and environmental. Each addresses specific vulnerabilities to ensure the harness’s reliability and durability.

Mechanical

Assesses the physical integrity of the harness, including tension, compression, and wear resistance, ensuring it can withstand operational stresses.

Electrical

Verifies the accuracy of connections, continuity, insulation resistance, and circuit functionality to prevent malfunctions and ensure proper power or signal transmission.

Environmental

Simulates conditions like temperature extremes, humidity, vibration, and chemical exposure to confirm the harness performs reliably in its intended environment.

Tools for Wire Harness Testing

Specialized tools are required to diagnose specific issues within a harness.

Test table

A test table is a dedicated fixture designed to hold the wire harness securely during testing. It is often customized to fit specific harness configurations, ensuring connectors and terminals are easily accessible.

Test tables streamline the process by keeping the harness organized, reducing handling errors, and enabling efficient testing of large or complex systems.

Multimeter

Multimeters measure key electrical parameters such as voltage, current, resistance, and continuity. They help verify the electrical integrity of individual circuits, ensuring that wires are correctly connected and components meet their specifications. 

Continuity tester

A straightforward yet essential tool, the continuity tester checks whether a circuit is complete by sending a small current through the wires.

It quickly identifies breaks, miswiring, or disconnected components and clearly indicates faults.

Proprietary modular testing systems

Proprietary modular testing systems represent the cutting edge of wire harness testing technology, offering versatility, efficiency, and precision.

These systems integrate hardware with advanced software, enabling automated testing, data collection, and analysis. 

Their modular design allows customization to accommodate specific wire harness configurations and testing requirements, making them ideal for industries requiring high reliability, such as aerospace, automotive, and manufacturing.

Here’s a look at some prominent proprietary modular testing systems:

• RTS—Known for their reliability and scalability, RTS systems are designed for high-volume production environments. They feature customizable modules to test a wide range of wire harness configurations, including continuity, high-voltage insulation, and resistance. RTS systems often include user-friendly interfaces and software for data analysis, making them suitable for production and quality assurance applications.
• Arcadia—Arcadia testing systems excel in flexibility and precision. They are equipped with advanced diagnostic tools to detect faults such as open circuits, short circuits, and incorrect pin configurations. Arcadia’s software-driven approach supports rapid reconfiguration for different harness designs, making it a preferred choice for industries with diverse product lines.
• TS1300—The TS1300 series is engineered for comprehensive testing, combining electrical, mechanical, and environmental assessments. It features high-resolution measurements and automated test sequences for maximum efficiency. The TS1300’s software allows seamless integration into existing production workflows, offering real-time reporting and detailed analytics for improved traceability and compliance.

Wire Harness Testing Methods

Wire harness testing begins with a visual inspection. When selecting the right parts and their quantities, consider the following:

• Wire color and gauge
• Cable length
• Proper registration of IDC cables
• Clean, contamination-free contacts
• Intact wires with no broken strands

Then, perform in-depth testing for troubleshooting accordingly. 

Short circuit test

This test identifies unintended connections between wires or components that could result in a short circuit. 

How to conduct the test:

• Connect between conductors supplying electrical power to a circuit using a multimeter 

• Place the multimeter on its continuity or resistance setting to confirm the voltage
• If there’s resistance lower than expected, then there’s a short circuit

High voltage test

Also known as a dielectric strength test or hi-pot test, it evaluates the insulation layer of the cable assembly. Essential for hybrids and electric vehicles (EVs), it ensures that the insulation can withstand extreme electrical stresses without defects, gaps, contaminants, current leakage, or short circuits.

How to conduct the test:

• Apply a voltage of approximately 10 kV between the two conductors. This voltage stresses the electrical insulation and soldered connections.
• Determine if your circuit can handle this high voltage for a short duration. If it passes, the assembly is deemed safe to operate at its standard voltage throughout its lifespan.
• A single hipot test machine can accommodate testing up to 20 conductors in multi-conductor cable assemblies. For assemblies with over 20 conductors, thousands of combinations must be tested, requiring multiple hipot machines.

Continuity testing

Continuity testing confirms that each circuit within the wire harness is complete and free of breaks. 

How to conduct the test:

• Connect the test points to a multimeter.
• The multimeter will send a voltage across the points and measure the circuit’s resistance. High resistance indicates a fault in the connection.
• If the circuit has electrical continuity, the multimeter emits an audible beep. For an open circuit, it will display an “open loop” message.

Resistance measurement with Milliohm tests: 

Measuring resistance helps verify the quality of connections and the suitability of the wire gauge.

Excessive resistance can indicate issues like loose crimps, corroded terminals, or undersized wires, which can impair performance and lead to overheating.

How to conduct the test:

• Use a milliohm meter that employs the four-terminal measurement method.
• Pass current through a segment of the assembly.
• Measure the voltage across one pair of terminals and the current through the other.
• The resistance between ground points should be about 2.5 ohms or less for proper electrical bonding. If it exceeds this value, the cable assembly is faulty.

Pull test: 

A pull test evaluates the strength of crimp joints, cables, mating connectors, and wires. During the test, the assembly is subjected to a certain load and rated based on the type of connector and wire used.

A motorized pull tester is employed to apply the pulling force and measure its value.

For instance, to verify if your cable can withstand a force of 50 pounds, use that force and check the cable for any signs of damage.

There are different ways you can perform pull tests:

• Pull and break: A destructive test where force is continuously applied to the cable till it fails, determining its maximum capacity.
• Pull and hold: non-destructive test where force is applied at a specific rate and maintained for a specified duration without causing damage.
• Pull, hold, and break: Another destructive method where force is applied and held at a specific rate. The force is gradually increased until the connectors fail or wires break.
• Pull and release: this is like the “pull and hold” method, but the applied force is removed after a specific rate, ensuring the assembly remains intact.

Bend/Flex test: 

Cable assemblies are often subjected to routing, flexing, and bending, which can damage them.

Flex cables are designed for applications requiring frequent twisting and bending while maintaining uninterrupted signal, data, and power transmission.

A flex/bend test assesses a cable’s suitability for such conditions.

• Secure one end of the cable to a bend or flex testing machine. 
• To the opposite end, add a weight or tie to a pretzel shape to create a 90-degree bend. 
• Alternatively, connect the cable to a swing arm mechanism that moves backward and forward in a semicircular or 180-degree arc. 
• Ensure the test follows a predefined min bend radius and the required number of cycles specific to the cable’s application.

IP66/IP67 water ingress test: 

Cable assemblies often adhere to two IP ratings, which manufacturers design to meet specific protection requirements: 

• IP 66: The first digit indicates complete protection from dust. The second signifies resistance to water from high-powered water jets sprayed from any angle.
• IP67: Similarly, the “6” represents protection from dust, while the “7” indicates the assembly’s ability to withstand immersion in water at depths of 15 cm to 1 meter for up to 30 minutes without water ingress.

Fungal resilience test: 

Humid and warm environments often promote fungal growth in assemblies, particularly in marine settings with extended exposure to darkness and moisture.

Fungal growth can cause aging, corrosion, and damage to the connectors, cable jackets, and conductors. To prevent such issues, the cable must undergo a fungal resistance test.

This is how you perform the test.

• A material coated with fungal spores is sprayed onto the cable.
• The cable is then placed in a chamber with humid and warm conditions.
• Frequent monitoring is conducted to observe fungal growth and measure its rate of development.

Best Practices for Wire Harness Testing

The electrical continuity test is the standard procedure for cable assemblies, ensuring proper connection between two devices.

Depending on the assembly’s application and the end customer’s requirements, additional tests, such as insulation and contact resistance, may be required.

For cable assemblies used in aerospace, medical, or automotive industries, specialized testing is essential to validate their performance and reliability. 

Wiringo has been a trusted name in the industry for over a decade, serving thousands of satisfied customers worldwide.

Wiringo specializes in producing high-quality wire harnesses tailored to meet diverse industry needs.

With a focus on precision manufacturing and rigorous quality control, Wiringo ensures that its harnesses exceed industry standards for reliability and performance.