A finished wire harness should be tested in three ways, because it can fail in three ways. Continuity testing proves the wiring is right: every net connects where it should and nowhere else. High-potential (HiPot) and insulation-resistance testing prove the insulation holds under voltage. Pull-force testing proves the crimped joints hold mechanically. Passing one says nothing about the others, so a test plan should cover all three families, with limits set from your product specification, not from a default. This guide explains what each method catches, which tests run on every unit and which are sampled, and what to put in your RFQ.
Updated October 3, 2026. An earlier version attributed specific test limits and section numbers to standards that do not set them, and cited a connector standard for crimp pull force; those have been corrected. Test voltages, thresholds and sampling plans come from your product specification and the standards you cite, so confirm them there.
1. Continuity testing: the electrical map
Continuity is the first and most basic test: does current flow along every intended path, and only along those paths. A tester energizes each net in turn and checks three things. The connection is present (no open), it goes only where the drawing says (no short or crossed wire), and its resistance is low enough (no high-resistance joint from a poor crimp). The resistance threshold comes from your specification.
Continuity catches errors the eye cannot: a terminal in the wrong cavity, two nets swapped at a connector, a poor crimp that reads high resistance. It is fast and non-destructive, so it is normally run on every harness. What it does not prove is that the insulation survives voltage or that a crimp survives being pulled.
2. HiPot and insulation resistance: the dielectric
HiPot (dielectric withstand) applies a voltage well above the working voltage between conductors, or between a conductor and a shield or chassis, for a fixed time and watches the leakage current. If the insulation is nicked, thin, contaminated or pinched, it can break down and leakage rises above the limit. The test voltage, duration and leakage limit are set by the product specification and the safety or performance standard that applies, so state them on the drawing or in the test plan instead of relying on a supplier default. HiPot is a stress test, so apply it where the application calls for it, such as multi-conductor, shielded or higher-voltage harnesses.
Insulation resistance (IR) applies a DC voltage and measures the resistance of the insulation in megohms. It indicates how healthy the dielectric is rather than proving a single withstand point, and a falling reading can warn of degradation. The test voltage and the pass floor, again, come from your specification. HiPot catches outright breakdown; IR can show degradation that has not yet reached breakdown.
3. Pull-force testing: the mechanical joint
A crimp is a mechanical and electrical joint formed by deforming a terminal around a conductor. It can read perfectly on continuity and still be under-crimped, holding now but ready to back out under vibration or a harness pull. Pull-force (crimp tensile) testing pulls the terminated wire until it separates and compares the force with a minimum for that wire and terminal.
The minimum comes from the terminal manufacturer's application specification and from the standards you build to. IPC/WHMA-A-620 sets workmanship acceptance criteria for crimped terminations, and automotive programs often add a terminal-to-wire crimp specification such as USCAR-21; the connector-system standard USCAR-2 covers the connectors themselves. Check the revision cited on your drawing, and do not copy a pull-force value from a different wire size.
Because the test destroys the sample, pull-force is sampled, not run on every unit. A typical plan samples at setup, at intervals, and after a crimp-die or terminal-lot change, and records the results on a control chart. It is backed by non-destructive checks on every unit, such as crimp-height measurement and visual inspection of the crimp, so the pull test shows that the process window is right and the other checks show that each unit sits inside it. See the crimping capability page for how the crimp process is set up.
How much testing? The acceptance class and the specification decide
The same harness can carry very different test scope depending on the acceptance class you specify. IPC/WHMA-A-620 defines three classes, general, dedicated service and high performance, and a higher class generally means tighter criteria, more inspection and more records. The class sets workmanship expectations, but the electrical test limits still come from your product specification. For what the classes mean and who chooses one, see the IPC/WHMA-A-620 guide; the wire choice also feeds the limits, covered in the wire gauge guide.
What to put in the test plan
- Net list or wire-to-wire list so the tester can be programmed directly.
- Continuity and resistance limits, and whether intermittent faults need to be checked.
- HiPot voltage, duration, ramp and leakage limit, and which nets or shields they apply to.
- Insulation resistance voltage and minimum.
- Pull-force minimums by terminal and wire, and the sampling plan.
- Records: what is logged, against what serial or lot, and for how long it is kept.
- Failure handling: what happens to a failed unit and to the lot it came from.
For the supplier's own equipment and limits, see the testing and inspection page, and compare them with your requirements before you rely on them. Methods only matter when they are run and recorded; ask to see a sample test record for a similar harness.
Representative project (anonymized to industry and region — no client name). An industrial-equipment OEM moving a harness program to a Cavite build was not worried about price; it was worried about intermittent field faults on the harness it was replacing. The qualification plan led with test evidence: continuity records, HiPot results, and pull-force sample charts on the first article, plus crimp-height logs. Seeing the actual data, not a certificate, was what let the OEM's engineers sign off and release the program. The lesson: for a reliability-driven buyer, the test report is the sales document.
FAQ
What is the difference between a continuity test and a HiPot test?
Continuity confirms the wiring is correct and low-resistance: every net connects where it should. HiPot confirms the insulation withstands a voltage well above the working voltage without breaking down. One checks the conductors, the other checks what separates them. A harness needs both.
Is every harness pull-force tested?
No. Pull-force is destructive, so it is sampled by wire size and crimp setup and recorded, not run on every unit. Every unit instead gets non-destructive checks such as continuity and crimp inspection. The sampling shows the crimp process is in spec; the unit checks show each harness sits inside that window.
Do I need the highest acceptance class?
Choose from the consequence of failure and the environment. A higher class adds inspection and records, which is worth it for safety-critical, medical or high-vibration programs and unnecessary cost for a general commercial harness. State the class and the electrical test limits in your RFQ so the plan and the price match the requirement.
What does a continuity failure usually mean?
Most often a terminal in the wrong cavity, two nets crossed at a connector, or a high-resistance crimp. Continuity localizes the fault to the net so the harness can be corrected and re-tested before it ships.
Have a harness with a defined test and acceptance class? Send the drawing, BOM and test scope through the RFQ page, and for a Philippines-origin program we will confirm the test plan alongside the build.
