WHAT YOU'LL NEED

• Screwdriver
• Replacement cord, plug, or socket
• Wire stripper with cutting blade or a knife
• Electrical tape
• Diagonal cutters

Lamp cord is known as zip cord. The #18 size is satisfactory for most lamp applications. Zip cord is available in many colors, the most common being black, brown, white, and transparent. Match the cord color to the lamp stand or the wall that holds the receptacle. The customary length is 6 feet, but you can use as much cord as you need to reach from the lamp to the receptacle.

To figure out how much cord to buy, calculate the length of the cord (including cord that is hidden in the lamp), and add 1 foot for attachments to socket and plug and for slack. In terms of safety and appearance, it's better to have an adequate length of cord than to compensate for a short one with an extension cord.

Remove the shade, unscrew the bulb, and squeeze the socket shell firmly at the switch while pulling on the top part to separate shell and cardboard insulator from the socket cap (usually you will see PRESS HERE on the socket).  If you plan to reuse the socket, do not use a screwdriver to pry the socket apart as that could damage it. 

Pull the socket out of the bottom shell as far as the attached wire permits. If this doesn't give you enough wire to work with, push the cord up from bottom of lamp for additional slack.  Loosen the socket's terminal screws, and remove the wires. If the lamp is small and the cord goes through in straight path, slide the old wire out, and feed new wire through from either end. If the old cord offers any resistance at all, don't tug on it. Check to see if you can disassemble the lamp to make removal easier. Also, check to see if the cord is tied in a knot to keep it from being pulled out at its base.

Twist the bare new and old conductor ends together, and fold twists flat along cord. Wrap a little electrical tape around the splice. Pull on the old cord from the top of the fixture, and work the new cord through; at the same time, push on the new cord from bottom  to help work it through. When you have sufficient length of new cord at the top, clip off the old cord.

 

Once you pass the new cord through the lamp, split the ends so you have about 3 inches of separated conductors. Use a wire stripper tool to strip about 3/4 inch of insulation from the ends of each conductor, then twist the strands of each together. Be careful not to nick strands when you strip the insulation. Tie an "underwriters knot" in the wire to act as a strain relief leaving enough wire above it to connect the lamp socket (See the photo below).

 

Bend the twisted end of each wire into a clockwise loop, and place each loop under the terminal screws on the socket with loop curled clockwise around screw. Tighten terminal screws. As each screw is tightened, clockwise the loop will pull the wire tighter under the screw head. (A counterclockwise loop would tend to loosen the wire.) See the second photo for how to get the polarity correct.

Clip off the excess bare wire with diagonal cutters. All uninsulated wire must be under the screw heads, with no loose strands or exposed bare wire. If bare wire is visible beyond the screw heads, unscrew the terminals, remove the wires, and re-do the connection.

Slide the insulator over the socket, and slip the shell over the socket and insulator. Then snap the shell into the cap.

Install a quick-clamp plug onto the other end of the cord. 

Stick the end of the cord into slot on side of plug, and push down on the lever at the top. Metal prongs inside the plug will bite through cord's insulation, piercing the copper wires to make the electrical connection. If you use a screw-type plug, prepare wire ends just as you did when making the socket screw connections, then knot them together. Loop each wire around the prong of the plug before tightening the bare end under screw head. Knots and loops keep wires from accidentally touching each other and also make it more difficult to loosen connections by pulling on the cord.