An electric plug (100; 200; 300) for connecting to an electrical module, which plug comprises: · an insulating body (110; 210; 310); · at least one connector pin (130, 131; 230, 231; 330, 331) that projects from said insulating body (110; 210; 310); and · locking means (150; 250; 350) for locking the insulating body (110; 210; 310) on the casing of said module; said locking means (150; 250; 350) comprising: · a movable portion (152; 252; 352) that is provided with fastener means (153; 253; 353) for fastening on the casing of said module, and a stationary portion that forms part of said insulating body (110; 210; 310), said movable portion (152; 252; 352) being mounted to slide on said stationary portion between a free position and a fastened position; and · a locking element (155; 255; 355) that is adapted to be mounted on said movable portion, at least in a locked position, in which it blocks said movable portion (152; 252; 352).in its fastened position on said stationary portion; the electric plug being characterized in that · said locking element (155; 255; 355) comprises a plunger (155; 255; 355) that is mounted on the movable portion (152; 252; 352) of said plug (100; 200; 300) to move in translation along an axis that is perpendicular to the axis along which said movable portion (152; 252; 352) slides, between said locked position in which it projects from said movable portion (152; 252; 352) into a slot in the stationary portion that receives it, and an unlocked position in which it allows said movable portion (152; 252; 352) to slide over said stationary portion, and in which it projects from said movable portion (152; 252; 352) through its top wall (152C; 252C; 352C); and in that • said plunger (155; 255; 355) includes blocking means (159, 160) that are adapted to block its movement in translation in each of its two positions. · an insulating body (110; 210; 310); · at least one connector pin (130, 131; 230, 231; 330, 331) that projects from said insulating body (110; 210; 310); and · locking means (150; 250; 350) for locking the insulating body (110; 210; 310) on the casing of said module; · a movable portion (152; 252; 352) that is provided with fastener means (153; 253; 353) for fastening on the casing of said module, and a stationary portion that forms part of said insulating body (110; 210; 310), said movable portion (152; 252; 352) being mounted to slide on said stationary portion between a free position and a fastened position; and · a locking element (155; 255; 355) that is adapted to be mounted on said movable portion, at least in a locked position, in which it blocks said movable portion (152; 252; 352).in its fastened position on said stationary portion; · said locking element (155; 255; 355) comprises a plunger (155; 255; 355) that is mounted on the movable portion (152; 252; 352) of said plug (100; 200; 300) to move in translation along an axis that is perpendicular to the axis along which said movable portion (152; 252; 352) slides, between said locked position in which it projects from said movable portion (152; 252; 352) into a slot in the stationary portion that receives it, and an unlocked position in which it allows said movable portion (152; 252; 352) to slide over said stationary portion, and in which it projects from said movable portion (152; 252; 352) through its top wall (152C; 252C; 352C); and in that • said plunger (155; 255; 355) includes blocking means (159, 160) that are adapted to block its movement in translation in each of its two positions.