A waterproof socket construction suitable for use in connecting an electric bulb to a lamp body therethrough on a motor vehicle. Included is a socket body having defined therethrough an axial hollow comprising a larger diameter portion extending rearwardly from the front end of the socket body and a smaller diameter portion adjacent the rear end of the socket body. A tubular, metal made ferrule is received in the larger diameter portion of the hollow and is locked against displacement relative to the socket body. An insulating plate having a foot contact thereon is mounted within the ferrule for axial sliding motion within limits. A cylindrical packing of elastic material is closely engaged in the smaller diameter portion of the hollow in the socket body for watertightly closing its rear end. The packing has a flange on its front end thereof held against the annular shoulder between the larger and smaller diameter portions of the socket body hollow. Disposed between the insulating plate and the packing so as to permit rearward displacement of the former relative to the ferrule, a spring forces the flange of the packing against the annular shoulder of the socket body for the establishment of watertight contact therebetween.