Pick a connector for internal PCB harnessing

This is the wiring that stays inside the box: power and signals leaving a PCB for fans, switches, motors, batteries, or another assembly. The enclosure protects it from weather, but vibration, bad latches, contact choice, tooling, and service mistakes can still ruin your day.

Use this when

• The connection is internal and protected by the enclosure.
• You want positive latches, polarization, and (in volume) secondary locks — not loose header pins.

Avoid this when

• The boards mount rigidly to each other and could plug together directly — see Board-to-board; a harness between rigidly-coupled boards is often the worse answer.
• The interface is external, sealed, or rugged — treat it as a sealed feedthrough or defense/rugged I/O unless the family is specifically sealed, latched, or potted; for budget sealed field wiring, the middle ground is rugged-on-a-budget.

Families to start with

• Molex Micro-Fit (and Mini-Fit / Nano-Fit) for internal power — its deep dive covers the Fit ladder, the terminal-set current, and the 30-cycle gotcha.
• PicoBlade / JST-GH and similar for signal — and note they are different 1.25 mm families that do not intermate; the GH page carries the lookalike table.
• TE and Harwin families where their ratings and latches fit.

One internal-power ecosystem can cover several physical jobs, but the similar-looking Fit families sit at different pitches and do not intermate. Measure and select the exact family before choosing the contact and tooling.

These are not "hobby" parts — professional versions have latches, polarization, secondary locks (TPA), and defined ratings. The dividing line is the specific family and rating, not the brand (see Major Connector Categories).

Search terms

• Micro-Fit wire-to-board latching connector crimp housing
• JST GH 1.25mm wire-to-board connector

Specs to check

• Current and wire gauge vs. the contact.
• Latch and TPA / secondary lock availability.
• Vibration exposure and whether the latch/lock is adequate.
• Tooling — the correct crimp tool and contacts for the exact family.
• Keying / polarization, especially in volume production.

Parts people forget

• Crimp tooling and the correct contacts for the family.
• The TPA / secondary lock and a keyed housing.

See What People Forget.

Common traps

• Pushing a hobby connector beyond its rating.
• Loose 0.1″ headers or bare solder joints where a latched, keyed housing belongs.
• No keying in volume production, so assemblies get cross-plugged.

Questions to ask a vendor/FAE

• What is the current/voltage rating of this exact family and contact?
• What crimp tool and contact part numbers are required?
• Is a TPA / secondary lock and a keyed/polarized housing available?

Example documentation bundle

• A selection table row for the harness.
• A source-controlled pinout with keying noted.
• A cable drawing and, for a controlled internal interface, an ICD entry.

Related: Decision Examples · Consumer / Hobby / Prototype connectors · for quick prototyping with pre-crimped leads and kit parts, the hobby track's Crimping and Marketplace Kits pages.