# Wedgelocks, TPA, and CPA: What Connector Secondary Locks Do

Learn the difference between terminal-position assurance, connector-position assurance, and family-specific wedgelocks—and how to specify them.

- Category: Assembly and validation
- Audience: Harness designers, assembly engineers, technicians, buyers, and students
- Published: 2025-11-14
- Updated: 2026-09-02
- Reading time: 8 minutes

## Direct answer

A TPA or family-specific wedgelock provides secondary assurance that terminals are fully seated and retained in the housing; a CPA provides assurance that the connector pair remains fully mated or that the primary latch is secured. Select each lock by exact housing MPN, side, position count, and key or modification, and never use a lock to force a partially seated terminal or connector.

## Key takeaways

- TPA acts at the terminal-to-housing interface; CPA acts at the connector-to-connector latch.
- Wedgelock is a family-specific implementation, not a generic size description.
- A lock that will not seat is a diagnostic signal, not an invitation for more force.
- BOMs and work instructions should name the lock and installation state explicitly.

## Three related terms, two different interfaces

**Secondary assurance devices**

| Term | Acts on | Primary purpose |
| --- | --- | --- |
| TPA | Terminal in housing | Confirm or reinforce terminal seating |
| Wedgelock | Terminal in selected connector families | Family-specific secondary retention/assurance |
| CPA | Mated connector latch | Secure or indicate full connector engagement |

## Why primary retention is not the whole story

Most crimp contacts have a lance or retention feature that engages the housing. Secondary locks add retention, position control, or an assembly check across multiple cavities. They help prevent a terminal from backing out when connectors are mated, vibrated, or serviced.

A CPA addresses a different failure: an incompletely engaged or released primary connector latch. Some designs use a sliding clip or lock that can only reach its final position after full mating.

## Select the exact lock

Distributor searches can group visually similar locks together. Use the housing drawing or family table and tie the lock MPN directly to its housing relationship.

- Match the connector family and product generation.
- Match plug or receptacle side.
- Match position count and cavity arrangement.
- Preserve key, color, and modification compatibility where applicable.
- Confirm whether the lock is supplied loose, pre-installed, or integrated.
- Check service and replacement requirements.

## Assembly sequence and failure signals

1. Insert each correctly crimped contact until primary retention engages.
2. Perform the specified light pullback or position check.
3. Inspect seal and terminal depth across all cavities.
4. Install the TPA or wedgelock using normal specified force.
5. If it stops early, remove and diagnose the affected cavity rather than forcing it.
6. Mate the connector fully, engage the latch, then install or close the CPA if present.

## Represent assurance in the design record

Include secondary locks in the BOM, show their final position in the assembly drawing, and define an inspection point. In a connector graph, attach the TPA or wedgelock to the specific housing and the CPA to the mating relationship it secures.

> Secondary assurance works only when it verifies correct primary assembly; forcing it can conceal the defect it was designed to expose.

## Frequently asked questions

### What does TPA mean on a connector?

Terminal Position Assurance. It is a secondary feature that helps confirm or reinforce correct terminal seating in the housing.

### What is the difference between TPA and CPA?

TPA addresses terminals retained in a housing; CPA addresses the connector pair and primary mating latch.

### Can I assemble a Deutsch DT connector without a wedgelock?

The specified wedgelock is part of the intended DT assembly and secondary retention system; include and install the correct one.

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