Electrical connector assembly, comprising: a plug connector, comprising a plug connector housing (10, 40) having a plug-in portion; a corresponding counter connector; and a spring operated secondary lock, being arranged movable on the plug connector housing in mating direction of the plug connector between an open position and a locked position; characterized in that the assembly further comprises at least one tension spring (30, 31) and the secondary lock comprises a spring attachment portion (21, 22) for the tension spring (30, 31) at its far end relative to the plug-in portion; and the plug connector housing comprises a spring attachment portion (15, 16) next to the plug-in portion; whereby the spring (30, 31) is attached with its respective ends at these respective spring attachment portions (15, 16; 21, 22) such that it is tensioned when the secondary lock is moved from the locked to the open position; and whereby the secondary lock further comprises an actuating portion adapted to be engaged by the counter connector during the mating process of the plug connector with the counter connector, so that the secondary lock is moved from the locked position to the open position upon mating; and whereby the engagement is released at the end of the mating process, such that the tension spring (30, 31) will pull the secondary lock back into the locked position. a plug connector, comprising a plug connector housing (10, 40) having a plug-in portion; a corresponding counter connector; and a spring operated secondary lock, being arranged movable on the plug connector housing in mating direction of the plug connector between an open position and a locked position; characterized in that the assembly further comprises at least one tension spring (30, 31) and the secondary lock comprises a spring attachment portion (21, 22) for the tension spring (30, 31) at its far end relative to the plug-in portion; and the plug connector housing comprises a spring attachment portion (15, 16) next to the plug-in portion; whereby the spring (30, 31) is attached with its respective ends at these respective spring attachment portions (15, 16; 21, 22) such that it is tensioned when the secondary lock is moved from the locked to the open position; and whereby the secondary lock further comprises an actuating portion adapted to be engaged by the counter connector during the mating process of the plug connector with the counter connector, so that the secondary lock is moved from the locked position to the open position upon mating; and whereby the engagement is released at the end of the mating process, such that the tension spring (30, 31) will pull the secondary lock back into the locked position. the plug connector housing comprises a spring attachment portion (15, 16) next to the plug-in portion; whereby the spring (30, 31) is attached with its respective ends at these respective spring attachment portions (15, 16; 21, 22) such that it is tensioned when the secondary lock is moved from the locked to the open position; and whereby the secondary lock further comprises an actuating portion adapted to be engaged by the counter connector during the mating process of the plug connector with the counter connector, so that the secondary lock is moved from the locked position to the open position upon mating; and whereby the engagement is released at the end of the mating process, such that the tension spring (30, 31) will pull the secondary lock back into the locked position.