A plug-in unit to be inserted in a housing carrying comb connectors of an electric motor, includes motor connectors (3) coupling with the comb connectors, and jacks (4) , which can be connected to an electric supply source of an electronic unit (7), connected to connection segments (3A, 4A) , connected electrically to the motor connectors (3) and jacks (4) . A body (2) of the unit (1) is made of plastic material and includes the motor connectors (3) and the jack connectors (4) partially embedded. Seal means (20) are integrated with the body (2) for sealing the unit (1) due to introduction into the housing. The electronic unit (7) is carried by a printed circuit board (5) featuring through seats (13A, 14A, 19A) for receiving the free ends of the connection segments . At least one of the free ends (9A) centers the board (5) with respect to the unit body, due to the coupling with a seat (19A) made in the board, to facilitate the introduction of the remaining ends of the connection segments (3A, 4A) into corresponding seats (13A, 14A) , for subsequent fastening by welding.