A Guide to Pull Testing and Quality Assurance for Wire Harness Terminations

Date Posted: 02/18/2026

When it comes to wire harness reliability, the way you terminate wires determines everything, from electrical performance to long‑term durability and safety. While crimp height and pressure are useful indicators, only a properly executed pull test reveals the true mechanical integrity of a crimped or welded connection.

What Makes a “Good” Termination?

A high‑quality termination starts before the test bench:

• Right materials: Match wire, terminals/contacts, and fittings to the application and spec.

• Right tools: Using DMC’s tool selection search find and use the correct crimp tool and die/locator/positioner. Ensure go/no‑go gaging is within tolerance.

• Right people & safety: Align tool choice with operator skill, volume, and wire sizes. Operator safety is non‑negotiable.

• Right process controls: For ultrasonic welds, maintain calibration and verification procedures.

Crimp Height vs. Crimp Pressure vs. Pull Testing

Crimp Height

• ✅ Non‑destructive and quick, great for in‑process checks.

• ❌ Cannot detect hidden defects (e.g., broken strands, poor strip quality, cracks, fractures).  Use it as one data point, not the final test.

Crimp Pressure

• ✅ Indicates equipment and operator performance where monitors exist.

• ❌ Not widely available on hand tools or many presses; may not be cost‑effective for small/medium shops. Use it where available, but don’t depend on it exclusively.

Pull Testing (Tensile Test)

• ✅ Resolves the mechanical integrity question and strongly correlates with electrical soundness.

• ✅ Works for crimped and welded terminations. This is your pass/fail control.
  

How Often Should You Pull Test?

There’s no one‑size‑fits‑all answer, but you can use this decision framework:

1. Contract/Customer Requirements

   • Automotive/aerospace often specify pull testing directly or through referenced process docs.

2. Applicable Industry Specs

   • Commercial/automotive: UL486A (Pullout Test, Section 12).

   • Aerospace: AS7928 (terminals), MIL‑C‑39029/AS39029 (contacts), MIL‑DTL‑22520 (tools), NASA‑STD‑8739.4 (space).

3. Manufacturer Guidance

   • Review connector/contact/wire/equipment literature for insights.

4. Historical Experience

   • If the termination is sensitive, equipment drifts, or past failures exist- test more often.

5. Quality Program Value

   • Will the data improve process control or reduce risk? If yes, increase frequency initially.

6. Cost of Testing vs. Cost of Failure

   • Rework, returns, and reputational damage are expensive. Testing is cheaper.

      

Destructive vs. Non‑Destructive Pull Testing

• Non‑destructive: Good for process monitoring in some contexts, but don’t use as a general QA measure for finished assemblies.

• Destructive: Required to validate adjustment/maintenance decisions and to clear setup changes.

• Test to minimum specified value (force-hold) or to separation (pull-to-fail).

• When testing to separation, record the separation mode (e.g., wire break outside crimp, pull‑out, etc.) for design/quality insight.

Pass/Fail Basics

• Pass if actual tensile value ≥ spec minimum for wire/contact size before break or test end.

• Separation type is typically not a pass/fail criterion, but it’s valuable data, especially during tooling/applicator setup. 

  • Typical separations

    • Wire Pull Out

    • Wire Break at Crimp

    • Wire Break Outside of Crimp

    • Wire Fray Break with Wire Break Outside of Crimp (Preferred)

• Aim for the joint to be stronger than the wire (break away from the crimp/weld). This may be unachievable with high‑strength alloy or nickel‑plated conductors (cold‑flow is limited; “gas‑tight” ideals diminish).

Calibration and Traceability (NIST)

• Use calibration labs that provide NIST traceability certificates.

• 12‑month calibration intervals are common.

• Prefer testers with built‑in calibration checks that run at every startup to flag drift between annual calibrations. DMC provides 2 tensile testers with built-in calibration:

• MPT-250C

• PT-150HA

Selecting the Right Pull Tester

Motorized vs. Manual

• Motorized: Required for spec compliance, controlled rate of pull (1 in/min ± 0.25), continuous force hold options, better repeatability, load‑cell protection (auto stop at max).

• Manual: Cost‑effective for in‑house setup verification; sensitive to operator technique (avoid “jerk”); consider audible max‑force alarms to protect load cells.

Range

• Match to your wire sizes and whether you test to minimum values or to separation (add ~25–50% headroom if breaking strength is required).

• Typical capacities:

  • Manual bench: up to 150 lbf (≈ AWG 12 Mil/Aero; AWG 6 commercial).

    • HPT-200B
    • PT-150HA

  • Small motorized: 200 lbf (≈ AWG 10 Mil/Aero; AWG 4 commercial).

    • MPT-250C

  • Larger motorized: 500 lbf (≈ AWG 4 Mil/Aero; up to 4/0 AWG commercial).

   

• Oversizing adds cost and may reduce sensitivity at lower ranges where most tests occur.

Grippers & Jaws (Critical!)

• Do not load the crimp/weld area as it can falsely elevate results. The grip point should be on the component. 

• For terminals/contacts:

• Slotted wheel grips are fast, repeatable, and avoid crimp compression.

• If no stable feature exists (weld nugget, thin stampings), use cam or threaded grips, train operators to avoid the joint area.

• For wire:

• Avoid single‑point pinchers.

• Use friction surfaces or wrap around a mandrel to distribute load and reduce “stress riser” breaks.

• Hard, slick aerospace insulations need careful grip adjustment to prevent slipping without damage.

Portability

• Battery‑powered portable testers are great for on‑line audits, supplier checks, and field support.

Why Not Just Use Weights?

• Traceability gets expensive (you’ll need certified, traceable weights).

• Safety risks: a slip or break can drop heavy masses. This can be hazardous and impractical.

• Lack of finesse: real tensile values rarely land on neat whole numbers, and accessories (hooks, grips) change net force.

Turn Test Data into a Competitive Advantage

In‑house pull testing becomes a real competitive advantage when a simple, operator‑friendly system delivers immediate, production‑floor feedback. Pairing a motorized digital tester with a guided workstation workflow, badge scan, job and tool selection, auto‑filled limits, instant pass/fail, turns each test into actionable process control rather than just a compliance step. Capturing a small but consistent data set (wire and terminal details, tooling, operator, spec reference, measured value, failure mode, and timestamps) ensures traceability and fast problem resolution, while networking stations lets quality, manufacturing, and engineering access results in real time. Even starting small and scaling up allows manufacturers to tighten feedback loops, reduce rework, validate tooling, and protect their reputation by proving termination integrity right on the shop floor.

In modern wire harness manufacturing, the pull test is the “final answer” on termination integrity. Crimp height and pressure tell you your process is behaving; tensile strength proves your connection will hold up in the field. With the right tester, grips, calibration discipline, and data strategy, you’ll reduce rework, satisfy compliance, and most importantly, protect your reputation with every harness you create. Ready to strengthen your process? Shop DMC tensile testers today.

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