single-wire seal, wire gasket, seal plug, blind plug, cavity seal, dummy plug
In a sealed connector the sealing is done in three places: an interface seal between the two mating halves, a wire seal on every populated cavity, and a cavity plug in every unpopulated one. Miss any one of them and the connector is no longer sealed, regardless of what its datasheet says.
Wire seals are sized to the wire, not just the terminal. The same TE MQS or Aptiv GT 150 terminal will be paired with different seal references depending on the insulation outer diameter, and the seals are usually colour-coded for exactly that reason. Fitting a seal outside its insulation diameter window gives either a seal that does not compress and lets moisture in, or a seal that will not enter the cavity and is forced, damaged, and lets moisture in.
Cavity plugs cause a specific, recurring procurement problem. They are cheap, low-priority line items that nobody watches, and they are the parts most often missing when a harness is otherwise ready to build. A connector with one open cavity in a wet or under-bonnet location is a warranty claim waiting on weather.
Seals and plugs also age. Elastomer parts have shelf-life guidance from the manufacturer, and stock pulled from a long-dormant channel should be date-code checked before use.
Harness Code treats seals and plugs as part of the connector set, not as an afterthought, and quotes the matching references when a housing or terminal is sourced.
Related terms
Sealed vs unsealed connector
A sealed connector uses interface seals, wire seals and cavity plugs to keep moisture and dust out, and carries an IP rating such as IP67 or IP69K. An unsealed connector has no such protection and is used only in dry interior locations.
Connector housing
A connector housing is the moulded plastic body that holds and positions the terminals of an automotive connector. It is sold separately from the terminals and seals it accepts, so a working connection is always a matched set of housing, terminal and seal, not a single part number.
Terminal / contact
A terminal, or contact, is the metal part crimped to a wire and inserted into a connector housing to make the electrical connection. Terminals are specified by family, gender (pin or socket), wire cross-section range, and plating, typically tin or gold.
Date code and lot code
A date code shows when a component was manufactured, usually as a year and week. A lot code identifies the production batch it came from. Together they let a buyer trace a part back through the supply chain and check that stock is genuine, recent and consistent.