An electrical assembly comprising: an electric plug including an insulating body and at least one connector pin that projects from said insulating body; and an electrical module (400; 500) comprising an insulating casing (480; 580) of generally rectangular parallelepiped shape, presenting a front face (411; 511) and an opposite rear face (415; 515), two parallel main side faces (410; 510) that extend over the height of the casing (480; 580), and two opposite transverse faces (413, 414; 513, 514), one of which includes at least one first opening (440, 441, 442, 443; 540, 541, 542, 543) giving access to an electrical connection terminal (417, 419), and at least one second opening (450A, 450B; 550A, 550B) giving access to an empty housing (451A, 451B; 551A, 551B), said second opening (450A, 450B; 550A, 550B) being arranged between said first opening (440, 441, 442, 443; 540, 541, 542, 543) and the front face (411; 511) of said casing (480; 580), and said empty housing (451A, 451B; 551A, 551B) of the module (400; 500) including mounting means that are adapted to co-operate with fastener means for fastening said electric plug to said casing (480; 580); the electrical assembly being characterized in that said electric plug includes locking means for locking its insulating body on the casing (480; 580) of said module (400; 500), which locking means comprise: · firstly both a movable portion that is provided with said fastener means that are adapted to co-operate with said mounting means of the module (400; 500), and also a stationary portion that forms part of said insulating body, said movable portion being mounted to slide on said stationary portion between a free position and a fastened position; and secondly a locking element that is mounted to move on said movable portion between an unlocked position in which it allows said movable portion to slide over said stationary portion, and a locked position in which it blocks said movable portion in its fastened position on said stationary portion. an electric plug including an insulating body and at least one connector pin that projects from said insulating body; and an electrical module (400; 500) comprising an insulating casing (480; 580) of generally rectangular parallelepiped shape, presenting a front face (411; 511) and an opposite rear face (415; 515), two parallel main side faces (410; 510) that extend over the height of the casing (480; 580), and two opposite transverse faces (413, 414; 513, 514), one of which includes at least one first opening (440, 441, 442, 443; 540, 541, 542, 543) giving access to an electrical connection terminal (417, 419), and at least one second opening (450A, 450B; 550A, 550B) giving access to an empty housing (451A, 451B; 551A, 551B), said second opening (450A, 450B; 550A, 550B) being arranged between said first opening (440, 441, 442, 443; 540, 541, 542, 543) and the front face (411; 511) of said casing (480; 580), and said empty housing (451A, 451B; 551A, 551B) of the module (400; 500) including mounting means that are adapted to co-operate with fastener means for fastening said electric plug to said casing (480; 580); · firstly both a movable portion that is provided with said fastener means that are adapted to co-operate with said mounting means of the module (400; 500), and also a stationary portion that forms part of said insulating body, said movable portion being mounted to slide on said stationary portion between a free position and a fastened position; and secondly a locking element that is mounted to move on said movable portion between an unlocked position in which it allows said movable portion to slide over said stationary portion, and a locked position in which it blocks said movable portion in its fastened position on said stationary portion.