A weatherproof light string employing a T-shaped inner frame with grooves to direct the placement of a plurality of conductors and apertures to secure conductive pins connecting conductors. The light string has secondary cables connected to the primary cables at one end and lamp holders at the other end. The insulation core wires at the first end of the secondary cable are positioned on the insulation core wires of the first cable by a T-shaped inner frame in a clamping and overlapping manner. Conductive pins extend through a side wall of the T-shaped inner frame and pierce the overlapped insulation core wires to from a mechanical and electrical connection between the wires. Light strings employing the T-shaped inner frame and conductive pins provide a more robust and reliable product, and are better suited to automation. Also disclosed is a method for manufacturing the light string.