An electrical connector assembly (10) of low profile for mounting onto a mother board (150), and having a housing (12) and an array of contacts (40) having elongate pin sections (42) insertable into through-holes (156) of mother board (150). The assembly includes a thin apertured organizer (50) movable along pin sections (40) and further includes a pair of guide posts (80) affixed to the housing (12) for example and extending through larger-diametered apertures (58) through organizer flanges (60) to leading ends (84) insertable into guide holes (154) of mother board (100). Organizer (50) abuts board (15) and is thereafter urged relatively toward and against housing (12) upon full mounting, being movable along guide posts (80) and pin sections (42). The assembly is accurately positionable with respect to the through-hole array by reason of the guide post leading ends (84) being received into guide holes (154) prior to pin section leading ends (44 ) entering through-holes (156).