To permit close positioning of a wire positioning finger (2) adjacent a slit blade insulation piercing connector, a pressing element (19) having a pressure surface (22) is movably located adjacent a wire outlet opening (10) of a wire guide duct (4) in the positioning finger. The pressing element (19) is movable, preferably longitudinally slidable on the finger, for movement transverse to the axis of the wire outlet opening between a quiescent position removed from the wire opening and a holding position to hold the wire (5) preparatory to cutting it off. A cutting knife (12) is movably located on the positioning finger (2), preferably slidable longitudinally, in the vicinity of the wire outlet opening (10) and movable between a rest position and cutting position in front of the wire opening. Respective pressing element control units (21) and knife operating control units (13) are provided, coupled to the pressing element (19) and to the knife (12) for programmed movement of the respective elements. Preferably, the pressing element (19) has a projecting portion (25) to counteract the tendency of a wire to curl as it leaves the wire outlet opening (10) from the positioning finger (2). The counter surface for the knife is formed by a wall (43) of the guide duct in the finger.