Dimmer switches replace standard light switches. They raise and lower the intensity of the light given off by light bulbs and turn the light fixture on and off. A standard light switch can be replaced by a dimmer switch, but the type of switch being replaced is important. Lights that can be turned on and off at two locations require three-way dimmer switches, and lights controlled at three or more locations will need two three-way dimmer switches and one or more four-way dimmer switches. One-way switches control lights from just one location.
Turn on the light controlled by the switch or switches you are replacing. Turn off the circuit breaker that controls the lighting circuit. The light should now be off and the circuit may be worked on safely.
Remove the cover from the light switch by removing the screws. Test the wiring with the no-contact voltage tester. If the tester is silent and does not light up when you bring the probe close to a wire, you have verified the current is off.
Remove the two screws that attach the switch to the wiring box. Gently pull the switch out of the box so it can be removed from the wiring. Notice the wires attached to the switch. Ground wires are bare or green and attach to a green grounding screw. The other wires all carry current.
Remove the two hot wires and ground wire from the one-way switch by loosening the terminal screws. One-way switches have two gold terminals, usually on the same side of the switch.
Place the two hot wires on the new one-way dimmer switch terminals. The wires should wrap clockwise around the screw. Place the ground wire on the green terminal screw the same way and tighten all the terminal screws firmly. It does not matter which hot wire you place on the gold terminals; either way will work fine.
Carefully place the wires back into the box behind the dimmer switch. Attach the switch to the box with the supplied screws. Replace the cover plate or install a new one and fasten it to the switch with the screws.
Note which wire is attached to the gold terminal and which two wires are attached to the nearly black terminals. The wiring order of three-way switches is important. Label the wire attached to the gold terminal with a piece of electrical tape. Loosen the terminal screws and remove the wires from the switch.
Place the labelled wire on the gold terminal on the dimmer switch and the other two wires on the nearly black terminals. Put the ground wire on the ground screw and tighten all the terminal screws firmly.
Neatly place the wires back into the box behind the dimmer. Add the screws to hold the dimmer in place and screw the cover plate over the dimmer switch. Fasten the plate to the box with the supplied screws.
Examine the wiring on the four nearly black terminals of the four-way dimmer switch. The two pairs of wires go to two different switches and each pair goes to the same switch. By looking at how the wires enter the wiring box, determine which two wires belong to each pair and mark one pair with tape. Remove the wires from the switch by loosening the terminal screws.
Examine the documentation supplied with the new four-way dimmer to determine which terminals are pairs. On some switches, the terminals on one side of the dimmer are a pair while the two on the other side are a pair. Other manufacturers place the terminal pairs on the ends of the switch.
Connect one pair of wires to one pair of terminals and the other pair of wires to the other pair of terminals. Put the ground wire on the green terminal screw. Tighten all the screws firmly.
Fold the wires into the box behind the dimmer switch as you push the switch into the wiring box. Screw the dimmer switch in place and put the cover plate over the dimmer switch and wiring box. Fasten the plate to the box with the supplied screws.
Be sure to install the dimmer switches so the slide goes up to increase the light intensity.
Always turn off the circuit breaker before working on an electrical circuit.