A harsh environment connector, comprising: a plug unit containing a contact pin having a forward end, a rear end, and an outer surface having a plurality of stepped portions (16, 17, 18, 19) of increasing diameter towards the rear end of the pin, each stepped portion including a respective annular electrical contact (11, 12, 13, 14), the plug contact pin being hollow and having an open forward end; a receptacle unit defining at least one contact chamber, a tubular receptacle contact module in said contact chamber having a rear end, a bore extending up to an open forward end configured to receive the plug contact pin and an inner surface having a plurality of stepped portions (153, 154, 155, 156) of decreasing diameter towards the rear end of the contact module which are of diameters configured for mating engagement with corresponding stepped portions (16, 17, 18, 19) of the pin, whereby the pin is in a close sliding fit in said contact module, each stepped portion (153, 154, 155, 156) having a contact seat and a respective annular electrical contact (147, 148, 149, 150) secured in said seat; the plug and receptacle units being movable between an unmated condition and a mated condition in which they are in releasable mating engagement with the contact pin in mating engagement in the contact module and each electrical contact on the contact pin in electrical communication with a corresponding electrical contact in the receptacle contact module to form a respective mated contact pair; the receptacle unit having an opening communicating with the contact chamber a which receives the plug pin as the units are moved into mating engagement; a seal assembly (129, 130, 132, 133) in the opening which is configured to seal the contact chamber in the unmated condition of the units and to form a seal against at least the outer surface of the plug pin in the mated condition of the units; and a centering rod in the receptacle unit extending through the receptacle contact module and having a forward portion located in the opening of the receptacle unit, the seal assembly comprising at least an annular outer seal (129, 130) in the opening configured for sealing engagement with the forward portion of the centering rod in the unmated condition of the units, wherein the centering rod is configured for mating engagement in the hollow plug pin in the mated condition of the units. a plug unit containing a contact pin having a forward end, a rear end, and an outer surface having a plurality of stepped portions (16, 17, 18, 19) of increasing diameter towards the rear end of the pin, each stepped portion including a respective annular electrical contact (11, 12, 13, 14), the plug contact pin being hollow and having an open forward end; a receptacle unit defining at least one contact chamber, a tubular receptacle contact module in said contact chamber having a rear end, a bore extending up to an open forward end configured to receive the plug contact pin and an inner surface having a plurality of stepped portions (153, 154, 155, 156) of decreasing diameter towards the rear end of the contact module which are of diameters configured for mating engagement with corresponding stepped portions (16, 17, 18, 19) of the pin, whereby the pin is in a close sliding fit in said contact module, each stepped portion (153, 154, 155, 156) having a contact seat and a respective annular electrical contact (147, 148, 149, 150) secured in said seat; the plug and receptacle units being movable between an unmated condition and a mated condition in which they are in releasable mating engagement with the contact pin in mating engagement in the contact module and each electrical contact on the contact pin in electrical communication with a corresponding electrical contact in the receptacle contact module to form a respective mated contact pair; the receptacle unit having an opening communicating with the contact chamber a which receives the plug pin as the units are moved into mating engagement; a seal assembly (129, 130, 132, 133) in the opening which is configured to seal the contact chamber in the unmated condition of the units and to form a seal against at least the outer surface of the plug pin in the mated condition of the units; and a centering rod in the receptacle unit extending through the receptacle contact module and having a forward portion located in the opening of the receptacle unit, the seal assembly comprising at least an annular outer seal (129, 130) in the opening configured for sealing engagement with the forward portion of the centering rod in the unmated condition of the units, wherein the centering rod is configured for mating engagement in the hollow plug pin in the mated condition of the units.