According to the On the House website, two parts on a lamp wear out occasionally: the cord and the socket. When a lamp no longer works, often the solution is to buy a new one. However, finding and diagnosing what is causing a lamp to quit working often takes only a few minutes. When a light socket doesn't work, eliminating any obvious causes is important. There are several minor tests you can perform to diagnose a bad light socket and what steps it will take to repair it.
Unplug the lamp from the wall outlet. Move the lamp to a stable work surface. Remove the lamp shade. Remove the lamp harp by squeezing the lamp harp sides toward one another and lift it up and out of the lamp harp base.
Locate the contact tab inside the base of the socket. It is the small metal tab it the bottom of the socket. Check for corrosion or rust, if found, scrape it from the contact with a flat-head screwdriver. Plug the lamp into the wall outlet, insert a light bulb and turn on the lamp. If the lamp does not light, unplug the lamp.
Check the contact to see if it is pushed too far down inside the socket and is not making any connection with the bottom of the light bulb. Pry the contact up using a flat-head screwdriver. Plug the lamp into the wall outlet, insert light bulb from the lamp on. If the lamp does not light, unplug the lamp.
Remove the socket to test it with an electrical tester by first pulling the exterior socket sleeve off the socket, exposing the wiring to the interior socket. Place a piece of black tape around the wire attached to the copper screw; this will help in identifying the hot wire for easier rewiring. Loosen the silver and copper screws located on each side of the interior socket and remove the wires from beneath them. Remove the socket. Use an electrical tester and touch one prong to the brass screw on the side of the socket and touch the other prong to the contact inside the socket. If your tester does not light up, you need to replace the socket.
Replace the socket by first wrapping the hot wire around the copper screw located on the side of the replacement interior socket and wrapping the remaining wire around the silver screw. Tighten both screws to hold the wires into place. Replace the exterior socket sleeve over the interior socket, pushing the socket sleeve firmly into the socket base.
Replace the lamp harp, light bulb and lamp shade.