With a dimmer, you may adjust light levels to create just the right lighting to fit your mood and enhance your home’s atmosphere. Equally important, dimmers save energy and make bulbs last much longer than they might at constant full power.
Shut off the circuit at the main service panel and take away the housing over the switch. Unscrew the switch and lift it out. If the box is metal, be particularly careful not to let the screw terminals on the side of the switch touch the box.
Test for power with a neon tester, probing one switch terminal and the bare grounding wire; repeat the test for the opposite terminal (see A). Proceed if the test light would not glow.
Cut off the wires on the switch terminals using wire cutters/strippers, and strip about 1/2 inch (12 mm) of insulation off the two cut switch wires.
Wire the dimmer. A dimmer with two black wires has no polarity, so twist each dimmer wire together with either one of the switch wires and screw on a wire nut (see B). If the dimmer has a green wire, connect it to the grounding wire.
If a dimmer has black and red wires, wire the black one to the incoming power (line) and red to the lights (load). To identify the wires, pull both switch wires out of the box; in case you have a plastic outlet box, pull out the bare wires, too. Keep them well aside from one another. Have someone restore power. Use a neon tester to probe one switch wire and the bare wire (or the metal box). If the tester glows, that’s the line, and the opposite wire is the load.