A method for making a supporting body (1) for the lock of a motor vehicle, including the steps of: forming an intermediate element (8) made of electrically insulating material provided with conductive paths (3); setting the intermediate element (8) inside a mold (23) for forming the supporting body (1); and injecting electrically insulating material in the mold (23) for carrying out co-molding of the supporting body (1). The intermediate element (8) and the conductive paths (3) are made independently, and the conductive paths (3) are fixed on opposite faces (9, 10) of the intermediate element (8) by constraint means (15, 16) of a mechanical type.