Open-barrel crimping done right
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Almost every connector in this shop — Metri-Pack, Superseal, JPT, MCP — uses open-barrel terminals: two pairs of wings folded around the wire by the tool. Done right, an open-barrel crimp is gas-tight and outlasts the car. Done wrong, it works on the bench and fails on corrugations. Here's the difference.
The anatomy of a good crimp
An open-barrel terminal grips the wire twice:
- Conductor crimp — the front wings fold into the bare strands. This is the electrical connection. The wings should roll inward into a B-shape (the classic "F-crimp" profile), with no strands escaping and no insulation trapped inside.
- Insulation crimp — the rear wings close around the insulation (or around the wire seal on sealed connectors). This is purely mechanical strain relief: vibration must never reach the conductor crimp.
Get the strip length right
Strip just enough that the bare conductor fills the conductor crimp with about half a millimetre showing on each side. Too short and the wings grab insulation; too long and bare strands stick out where they can short or wick moisture. A calibrated stripper beats a knife every time — nicked strands lose cross-section and fatigue-break.
Match terminal, wire and tool
Every terminal has a rated wire range — for example, a Superseal 1.5 contact takes 0.75–1.5 mm². Crimping 0.5 mm² into it gives a loose, high-resistance joint no amount of squeezing fixes. The same goes for the tool: use a ratchet crimper with the correct die profile, which completes the full cycle every time. Pliers, "universal" crimpers and vice-grips deform the barrel instead of rolling it.
The five classic mistakes
- Soldering a crimp "for extra strength". Solder wicks up the strands and creates a hard spot right at the strain-relief point — that's where it snaps under vibration.
- Insulation in the conductor crimp. Looks fine, measures fine, fails warm.
- Wrong wire size for the terminal — see above.
- Skipping the pull test. Give every crimp a firm tug. A correct 0.75 mm² crimp survives more force than you can apply by hand.
- Reusing terminals. Once crimped, the barrel's work-hardened. Cut it off and fit a new one — they cost cents.
Sealed connectors: don't forget the seal
On sealed systems (Superseal, JPT, MCP) the rear wings crimp around the wire seal, not the insulation. The seal must match your wire's insulation diameter — more on that in our wire seal guide.
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