A wire harness that leaves the production floor untested is a liability waiting to happen. Testing is the final—and arguably most important—quality gate in wire harness manufacturing. It verifies that every connection is correct, every crimp is secure, and the harness will perform safely under its intended operating conditions. This article covers the principal testing methods used in the industry and explains why each one matters.
Continuity Testing
Continuity testing is the most fundamental check in harness validation. It confirms that every conductor connects the correct points and that no unintended connections (shorts) exist between circuits. A low-voltage, low-current signal is sent through each wire path to verify that the resistance falls within acceptable limits—typically below 1 ohm for a properly crimped and routed connection.
Modern automated test systems can verify hundreds of connection points in seconds using bed-of-nails fixtures or connector-mating adapters. The test program maps every expected connection and flags any opens (missing connections), shorts (unintended bridges between circuits), or miswires (conductors routed to the wrong pin). For a 100-percent production test, continuity testing is the minimum acceptable standard. Detailed definitions of these testing terms and more can be found in our wire harness glossary.
High-Potential (Hi-Pot) Testing
High-potential testing, commonly called hi-pot or dielectric withstand testing, applies a voltage significantly higher than the harness’s rated operating voltage between conductors and between conductors and any shielding or grounding points. The purpose is to verify that the insulation can withstand voltage stress without breakdown.
A typical hi-pot test applies 1,000 V AC plus twice the rated working voltage for one minute, though specific standards vary by application. For a 300 V rated harness, this would mean a test voltage of 1,600 V AC. The test instrument monitors leakage current during the stress period. If the current exceeds a predetermined threshold, the insulation has failed and the harness is rejected.
Hi-pot testing is mandatory in many safety-critical applications including medical devices, industrial machinery, and any product requiring UL, CSA, or IEC safety certification. Our quality certifications page outlines the standards we comply with during production testing.
Insulation Resistance Testing
While hi-pot testing checks whether insulation can survive a voltage spike, insulation resistance (IR) testing measures the actual resistance of the insulation material under a DC voltage—typically 500 V or 1,000 V DC. Results are expressed in megaohms (MΩ) or gigaohms (GΩ).
Healthy insulation on a new harness should measure in the hundreds of megaohms to gigaohms range. Lower readings indicate moisture absorption, contamination, or insulation damage. IR testing is particularly important for harnesses that operate in humid or wet environments, such as outdoor energy installations or marine applications, where insulation degradation could lead to dangerous leakage currents over time.
Pull-Force Testing
A crimp or solder joint is only as good as its mechanical retention. Pull-force testing (also called pull-out or tensile testing) applies a controlled axial force to a terminated wire to verify that the terminal will not separate from the conductor under stress.
The required pull-force values are specified by the terminal manufacturer and depend on the wire gauge and terminal type. For example, a typical crimp terminal on AWG 18 wire might require a minimum pull-force of 35 N (approximately 8 lbf). Testing is performed on a calibrated force gauge or automated pull tester that applies force at a controlled rate until either the minimum threshold is reached (pass) or the termination fails (reject).
Pull-force testing is usually performed as a destructive sample test—for instance, the first and last termination of each setup, plus periodic samples during a production run. It is a key requirement of IPC/WHMA-A-620, the industry standard for wire harness workmanship. For more on common testing questions, visit our FAQ page.
Crimp Cross-Section Analysis
Crimp cross-section analysis (also called micro-section analysis) is the most thorough way to evaluate the quality of a crimp termination. A crimped terminal is cut perpendicular to its axis, mounted in epoxy resin, polished, and examined under a microscope.
The cross-section reveals critical details: the shape of the crimp barrel after compression, the distribution of wire strands within the barrel, whether any strands are cut or displaced, and the percentage of void area (empty space) within the crimp zone. Industry standards like IPC/WHMA-A-620 specify acceptable crimp heights, widths, and void percentages for various terminal types.
This is a destructive test used during process validation and periodic quality audits rather than on every production piece. It is essential when setting up a new crimp tool, qualifying a new terminal-wire combination, or investigating a field failure.
Additional Testing Methods
Beyond these core methods, specialized applications may require additional tests. Seal integrity testing verifies that sealed connectors meet their IP rating by applying air pressure and checking for leaks. Flexure testing subjects harnesses to repeated bending cycles to validate durability in dynamic applications. Thermal cycling exposes harnesses to alternating temperature extremes to accelerate aging and detect latent defects.
Building a Complete Test Strategy
An effective test strategy combines 100-percent electrical testing (continuity and, where required, hi-pot) with statistical sampling of mechanical tests (pull-force and crimp cross-section). The specific mix depends on the application’s risk profile, applicable standards, and customer requirements. Safety-critical automotive, aerospace, and medical harnesses demand the most rigorous protocols, while consumer electronics may require a lighter approach.
At SIMKAB, testing is built into every stage of our manufacturing process—not treated as an afterthought. From incoming material inspection through final electrical verification, we ensure every harness meets its specification before it ships. Learn more about our commitment to quality on our quality certifications page, or request a quote to discuss your testing requirements with our engineering team.