Abstract: In a method of manufacturing a moulded-on mains plug of the type having a base 3, an insulating cap 1 covering wire connection points 9, and a moulded-on plug body, the presence and position of the cap 1 is detected by probe pins 37,39 of a pressure member 31 coupled to a position detector 47. The arrangement is such that the moulding material can only be injected into the moulding die 27,29 if the cap 1 is substantially in its correct position as shown in FIG. 2. In this way, it is not possible to produce a moulded-on mains plug having no insulating cap or in which the cap is provided but is incorrectly positioned.