A plug-in connector for connecting to a receptacle, the connector comprising: a housing (18,19,20) including at least one fin; at least one electrically conductive terminal at least partly situated in said housing (18,19,20) and defining a mating axis and a mating direction, said electrically conductive terminal being configured to electrically connect to a conductor of a cable or wire to be terminated by the connector; at least one cantilevered locking beam arranged in said housing (18,19,20); a slider slidingly coupled to said housing (18,19,20) and including at least one blocking beam extending in the mating direction; and a compressive member arranged to urge said slider outward away from said housing (18,19,20) in the mating direction, and wherein, when moving the housing (18, 19, 20) into the receptacle, said at least one blocking beam is adapted to abut against a bulkhead surface of the receptacle during a first intermediate stage of relative movement between said housing (18,19,20) and said slider against a bias of said compressive member to cause said compressive member to be compressed, and said at least one fin is situated to abut against a respective one of said at least one blocking beam during a second intermediate stage after the first intermediate stage of the relative movement while allowing inward deflection of said respective one of said at least one cantilevered locking beam to pass outward of a respective one of said at least one blocking beam into engagement with the receptacle, and in a final stage of the relative movement between said housing (18,19,20) and said slider after the second intermediate stage of the relative movement, each of said at least one cantilevered locking beam is adapted to pass into a respective locking site of an undercut of the receptacle and said at least one fin is adapted to urge the respective one of said at least one blocking beam outward to enable said blocking beam to move to a position inward of the respective one of said at least one cantilevered locking beam and prevent release of said cantilevered locking beam from the respective locking site, and wherein said at least one blocking beam is configured to prevent inward deflection of the respective one of said at least one cantilevered locking beam after the final stage of the relative movement between said housing (18, 19, 20) and said slider, and the connector is adapted to have an electrically interconnected state only when in the final stage. a housing (18,19,20) including at least one fin; at least one electrically conductive terminal at least partly situated in said housing (18,19,20) and defining a mating axis and a mating direction, said electrically conductive terminal being configured to electrically connect to a conductor of a cable or wire to be terminated by the connector; at least one cantilevered locking beam arranged in said housing (18,19,20); a slider slidingly coupled to said housing (18,19,20) and including at least one blocking beam extending in the mating direction; and a compressive member arranged to urge said slider outward away from said housing (18,19,20) in the mating direction, and wherein, when moving the housing (18, 19, 20) into the receptacle, said at least one blocking beam is adapted to abut against a bulkhead surface of the receptacle during a first intermediate stage of relative movement between said housing (18,19,20) and said slider against a bias of said compressive member to cause said compressive member to be compressed, and said at least one fin is situated to abut against a respective one of said at least one blocking beam during a second intermediate stage after the first intermediate stage of the relative movement while allowing inward deflection of said respective one of said at least one cantilevered locking beam to pass outward of a respective one of said at least one blocking beam into engagement with the receptacle, and in a final stage of the relative movement between said housing (18,19,20) and said slider after the second intermediate stage of the relative movement, each of said at least one cantilevered locking beam is adapted to pass into a respective locking site of an undercut of the receptacle and said at least one fin is adapted to urge the respective one of said at least one blocking beam outward to enable said blocking beam to move to a position inward of the respective one of said at least one cantilevered locking beam and prevent release of said cantilevered locking beam from the respective locking site, and wherein said at least one blocking beam is configured to prevent inward deflection of the respective one of said at least one cantilevered locking beam after the final stage of the relative movement between said housing (18, 19, 20) and said slider, and the connector is adapted to have an electrically interconnected state only when in the final stage.