Rewiring a Lamp
Source: Martha Stewart Living, September 1996
The first step of repairing any electrical appliance is to find the problem. If your lamp doesn't turn on, check that it is plugged into a working outlet and that the bulb is good. Then check the cord and the plug for damage (if the cord is damaged, skip the next paragraph and follow the steps for changing a cord; for more on changing a plug, see "Replacing a Plug"). If the cord and plug look good, the next step is to test the socket.
Before testing the socket, unplug the lamp, and remove the lightbulb. Squeeze the socket shell where the word PRESS is imprinted, and lift it off (some lamps will have a small setscrew that needs to be loosened before you can lift off the shell). Lift out the insulating sleeve, loosen the terminal screws, and disconnect the wires. Now, use a continuity tester to test the socket: Attach the tester's clip to the metal part of the body, and touch the probe to the silver terminal screw. If the tester lights, the socket is good. The socket switch may be bad, however, so test it next: Attach the clip to the brass terminal screw, turn the switch to the "on" position, and touch the tester's probe to the round tab inside the socket. If the socket is good, the tester will light. If the socket or switch is bad, buy a new socket just like the old one. Skip to the final paragraph to learn how to rewire the socket.
If the tested socket is functional, but the lamp still doesn't work, it's time to change the cord. (Any cord that is obviously damaged or worn should be changed, even on a working lamp.) First, disconnect the socket, if you haven't done so already, by detaching the wires from the terminal screws. Cut the old cord somewhere between the plug and the base of the lamp. Cords comprise two insulated wires, joined at the middle. Split the top two inches of the new cord down the middle, and use a wire stripper to strip half an inch of insulation from each wire. Repeat this process on the old cord. Twist the old wires and new wires together with a Western Union splice; attaching the two cords will allow you to thread the new cord through the lamp. To make the splice, make an X shape with two exposed wires, one from the new cord and one from the old; twist the wires together until you've made a single row of tight little coils (they should look like the coiled rope on a noose). Repeat with the remaining two wires. A Western Union splice, when covered with electrical tape, should be able to slip through a lamp stem or chandelier arm. Pull carefully at the top of the old cord where it emerges from the socket (photo 1, bottom left), and thread the new cord through. When the new cord is visible, disconnect the old cord, and discard it. If there is enough room in the cap, tie the ends of the new cord's wires into an underwriters' knot (photo 2), which will prevent the cord from being pulled free of the socket by a tug or a jerk at the other end.
To rewire an old working socket to a new cord, or to wire a new socket, first wrap the neutral wire (covered with ridged insulation) clockwise around the silver terminal screw, and tighten (photo 3); then wrap the smooth, hot wire clockwise around the brass terminal, and tighten. Test the connections on the socket with a continuity tester. Snap the socket body into place; replace the sleeve and the shell. Plug in your newly rewired lamp, and turn it on.
Replacing a Plug
Plugs that are cracked, discolored, or warm to the touch when in use should be replaced. Two types of replacement plugs are available: self-clamping plugs and screw-on plugs. Self-clamping plugs are simple to install, but they will not accept cords of every shape and size. To avoid choosing the wrong kind, you may need to ask for help at an electrical supply store when matching a plug to a cord. Changing plugs for large appliances can be complicated, so amateurs should change only lamp, radio, clock, or other small-appliance plugs. New plugs should only be attached to new or undamaged cords.
To install a self-clamping plug (1), cut off the cord at a right angle near the old plug (or further up if there is cord damage). Then open the shell of the new plug. Slip the wire into the shell from behind, and clamp the prongs shut; replace the shell. You don't need to strip the insulation from cords inserted into self-clamping plugs.
To install a screw-on plug (2), pry the insulating disk from the prongs. Strip the new wire back half an inch, and solder or twist the strands together tightly. Insert the twisted or soldered wire into the plug from behind, and wrap each wire so it goes around a prong for support before it is attached to its terminal screw. Be sure that exposed wires do not touch. If one prong of the plug is larger than the other, the plug is polarized: Connect the positive wire (with a smooth casing) to the brass terminal screw of the smaller prong; connect the neutral wire (with a ridged casing) to the silver terminal screw of the larger prong. Replace the insulating disk. Plug in the lamp, and turn it on.
Most table lamps do not draw dangerous levels of electrical power; but the aspiring lamp maker should follow these simple safety rules:
Always shut off the power at the service panel to the light fixture you are working on; always unplug a lamp before working on it.
If you remove a fuse, keep it with you so it can't be replaced while you're working; when you shut off a circuit breaker, tape over the breaker, and close the panel door. Tape a sign to it reading: Do not touch! These steps reduce the chance that someone will unwittingly turn the power back on.
Always use wooden or fiberglass ladders; aluminum and metal ladders are not insulated and might conduct electricity.
Use only tools with insulated handles.
Use lightbulbs that are the proper wattage for your lamp or light fixture. A bulb whose wattage is too high may overheat.
Don't touch metal pipes while you make electrical repairs.
Water and electricity are a dangerous combination. Wear rubber-soled shoes when making electrical repairs; stand on a dry rubber mat or wooden boards if the floor is wet.
When opening the service-panel door, keep one hand at your side so you won't touch something that will create a complete circuit if there is current leaking from the panel.
Before starting to work on a light fixture, always test the fixture with a voltage tester to be sure the power is off.
Loop wires clockwise around terminal screws; this will keep the wires from coming off as the screws are tightened.
If your house is older, have an electrician check to be sure that all receptacles and direct-wired appliances are grounded.
Don't change any fixtures if your house has aluminum wire (either aluminum or reddish color), as it could be dangerous. Call an electrician to replace the wire ends. Copper or copper-coated wire is safe to work on.