Abstract: A locking device for plug and socket type electrical connectors includes a flexible nonconductive pin for insertion through the socket cover plate and the socket body of a recessed wall type socket connector member or a socket connector member disposed in an enclosure which prevents insertion of the pin in a direction generally normal to the direction of engagement of the plug with the socket member. A guide tube is disposed between the socket body and the socket cover plate for guiding the pin through essentially a right angle turn so that the pin may be inserted in and removed from the socket from the plane of the cover plate. The pin includes an elastically deflectable shank portion and a head having a tool engaging part and a threaded shank part for engagement in an internally threaded bore in the socket cover plate or a bushing insert disposed on the socket cover plate.