From time to time wall switches fail when the contact points within the switch become worn or eroded. If a switch doesn't work, first make sure the problem is with the switch and not the light or device it's supposed to power. Plug a working lamp or other appliance into the switch-controlled receptacle to make sure the switch is faulty.

It's easier and cheaper to replace a switch than it is to repair it. Be aware that you don't need to replace it with the same kind of switch. For example, you might want to replace a single-pole switch with a dimmer switch to save energy and vary the lighting in a room to suit your needs. Both are attached to a ground, are wired into "hot" wires only, and have either terminal screws or lead wires for making connections. (You can't, however, simply replace one switch with another type that requires more wires--a single-pole switch with a three-way switch or sophisticated lighting controls, for example.)

When you replace a switch, make sure you check the amp and voltage ratings on the back of the old switch. The new switch should have the same ratings.

If you have aluminum wiring (the metal part of the wires looks silvery), be sure to get a replacement switch marked CO/ALR. Unmarked or CU/AL switches should be replaced with CO/ALR switches.

To replace a switch:

1) Shut off the power at the circuit breaker and test the bare ends of connection wires with a circuit tester to be sure the power is off.

2) Carefully unscrew the switch from the electrical box, pull it outward without touching any bare wires, and test the bare wire ends again to make sure they're not active.

3) Remove the old switch by disconnecting the wires from its terminals. If the wires are attached to screw terminals, just loosen the screws by turning them counterclockwise. If the wires are pushed into terminal holes in the back of the switch, press a very small-headed flat screwdriver into the small rectangular slots located by the terminal holes to release the wires.

4) Loosen the green grounding terminal screw and, using needle-nose pliers, loop the bare or green wire grounding wire from the circuit around it, clockwise, and tighten the screw to lock it in place. Then, if the switch has terminal screws, loop the circuit wires clockwise around the terminal screws in the same fashion and tighten the screws. If the switch only has push-in terminal holes in its back, make sure that 1/2-inch of insulation is stripped from the end of each circuit wire, straighten the tip with lineman's pliers, and push the wires into the terminal holes. Wiggle all wire connections to make sure they are secure.

5) If the new switch has short wires coming out of its body connect the twist the bare end of the green wire together clockwise with the circuit's green or bare ground wire, using lineman's pliers, then secure the connection with a wire nut. Then join the bare ends of the switch's wires to the circuit wires, twist clockwise, and secure them with wire nuts. Wiggle wires to make sure connections are secure.

6) Push the wires and switch into the wall box, and then place the flange of the switch over its screw holes in the box. secure the flange with screws at the top and bottom, and put a face plate over the wall box.

7) Turn the circuit back on and test the switch.