How to Fit Dimmer Switches

Replace light switches with dimmer switches for interior ambient lighting. Dimmer switches come in multiple sizes and styles. They can add a new feel to current room decor, or be part of a remodelling project to change up the look of a home or room. Older dimmer switches consisted of a plate, that resembled the light switch plate, and a knob-like dial that allowed the lights to turn on at various levels providing very low amounts of light and gradually increasing to full strength. Newer models of dimmer switches include a sliding switch and large, flat switches.

Measure the current light switches by using the measuring tape to determine the size of the light switch plate; the plastic or wood rectangular plate that attaches to the wall supporting the light switch. A typical single-switch light switch plate may measure 3.5-by-5.5 inches, for example. Write these measurements down for all switches that you will replace, then note whether the current switch has one, two or more light switches.

Purchase the desired dimmer switches (design preference) that fit, or are slightly larger than, the measurements of the previous light switches. This is important because if the dimmer switch plate is smaller than the current light switch plate, it is possible the wall behind it is not painted completely and this will show. The hole where the wires come out of the wall can also show.

Turn the power off for the room where a dimmer switch is to be installed. If the room contains more than one circuit breaker switch, be sure to turn off at least the circuit breaker for the switch you are replacing.

Remove the light switch plate using a flathead screwdriver. Remove the screws that hold the light switch in place; these are behind the switch plate, generally screwed into the wall or into the wall through a metal guide. Carefully pull the switch out of the hole in the wall, exposing the wires behind it.

Inspect, visually, the two black wires connecting to the light switch. If the copper ends are worn or old, it is best to cut the ends and strip about a half-inch from the black wire coating for fresh copper ends. If the copper ends seem in good condition, reuse them with the new dimmer switch.

Connect the ground wire to the ground pigtail on the new dimmer switch. The ground wire is usually coated in green and located in the wall with the two black wires. You'll find the ground pigtail on the back of the dimmer switch; it is usually copper. There will also be two black pigtails on the dimmer switch which you need to connect to the black wires using wire connectors.

Push the wires and the new dimmer switch into the hole in the wall, and secure the dimmer switch with screws as the previous light switch had been. Put the dimmer switch plate on, following manufacturer's instructions and diagram from the packaging, and secure with screws or as directed.

Turn the power back on to that switch or room. Test the dimmer switch by turning the lights on, and checking the various dimming levels using the new switch.


Ensure the wire ends are concealed within the wire connectors for electrical safety. Always have another adult present when working with tools or electric parts and appliances.

Things You'll Need

  • Tools
  • Measuring tape
  • Dimmer switch
  • Wire cutters
  • Wire connectors
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About the Author

Sasha Maggio specializes in topics related to psychology, fitness, nutrition, health, medicine, dentistry, and recovery after surgery, as well as cultural topics including Buddhism, Japanese culture, travel, languages and cooking. She holds a Bachelor of Arts in psychology and Japanese from the University of Hawaii, as well as a Master of Arts in forensic psychology. She is currently pursuing Medical and PhD programs.