Abstract: An electrical connector system includes a plug connector and a secondary locking device. The plug connector mates with a corresponding counter connector and includes a plug connector housing having a terminal cavity for receiving an electrical contact terminal. The secondary locking device provides a secondary locking function when the plug connector mates with the corresponding counter connector and when the secondary locking device is in a closed position. The secondary locking device is movable relative to the plug connector housing from an open position to the closed position. The secondary locking device has a stem portion and a flexible leg. The stem portion extends in the closing direction. The flexible leg has a fixed end and a free end. The flexible leg connects to the stem portion at its fixed end. The flexible leg extends from the fixed end to the free end opposite the closing direction.