Replacing a Dimmer Switch

Written by Allen Wyatt (last updated September 2, 2019)


Whether you are preparing for a romantic dinner for two or working on an important deadline in the middle of the night, you will find that a working dimmer switch is crucial in properly controlling the lighting in your home. A dimmer switch can be attached to almost any internal lighting in your home in order to vary the brightness or dimness of lighting. A dimmer switch works by increasing or decreasing the amount of power being supplied to the light in order to brighten or dim it. Some dimmer switches are knobs and others have sliding mechanisms.

Dimmer switches are most often used with incandescent lighting fixtures, not with fluorescent fixtures or many of the newer CFL or LED lights. It is possible that some non-incandescent fixtures will allow you to use them with a dimmer, but you'll want to check with the manufacturer to see if this is the case. If you use a dimmer with a fixture that doesn't support the variable power supplied by a dimmer, then you run the risk of malfunction, which isn't good with electrical devices—it could even cause a fire!

Of course, if you already have a dimmer in place and all you need to do is replace it, you are probably safe—you only need to be concerned with the fixture if you are installing a dimmer switch for the first time or if you are replacing the fixture itself.

In order to replace or install your dimmer switch you will need a few items. Search your home, local hardware store, or ask your friendly neighbor for a circuit tester, wire nuts and a set of flathead screwdrivers. Using the circuit breaker or fuse box—generally located in the garage, basement, or laundry room—turn off the power to the fixtures that are controlled by the switch. Test the lights in the room by flipping various switches in order to ensure that the power is off. (When you work with electricity, it is important to take a variety of safety precautions like this one.)

Locate the switch that needs to be fixed or replaced and remove the cover. The cover is a piece of plastic or metal that attaches to the wall to protect the light switch and provide an aesthetically pleasing facade. The cover is typically held in place by one or two small screws visible from the front of the cover plate. Remove them, and you should be able to pull the cover right off.

  • If the dimmer switch uses a knob, it is possible that the knob will block the removal of the cover plate. In this case, a firm pull on the knob—straight out, away from the wall—should remove the knob and allow you to easily remove the cover plate.
  • If the room was painted by someone who didn't remove the cover plate before painting, it is possible that the dried paint will keep the cover plate "attached" to the wall. If this is the case, carefully use a sharp knife to score the paint at the edges of the cover plate. This should allow you to remove the cover plate without damaging the wall.

With the cover plate removed, you should be able to see the screws that actually hold the switch in the electrical box. In almost all instances there are two of these screws—one near the top of the switch and one near the bottom. Unscrew both of these completely and gently pull the switch assembly out of the electrical box itself. Suspend the switch a few inches away from the wall so that the wires are exposed.

Take a moment to examine the switch so that you are familiar with how the wires are connected. In most modern installations, a single-pole switch will have only three wires that connect to the switch—one white, one black, and one green. The green is the ground wire; it is the white and black wires that actually carry power. Take note of which wires are connected to which screws and then remove the wires from the old switch.

Important: If the switch you are replacing has more than three wires to it, it is probably a three-way or four-way switch. These types of switches have more complex wiring, as they work in conjunction with other switches to control the lights. For instance, you may have a room where there are two doors and a switch for the lights by each of the doors. If you are replacing this type of switch, you need to make sure your new switch matches the characteristics of the old one. Mark which wires were connected to which screws on the switch, remove it from the wires, and take it to the hardware store to get a matching replacement switch.

With your notes about which wires were attached to which screws on the old switch, connect the wires to the same screws on the new switch. It is possible that the dimmer switch will not have screws, but will instead have wires already attached to the switch. If this is the case, connect the wires for your home to the appropriate wires on the switch using wire nuts and electrical tape.

With the wires securely fastened to the switch, gently push the switch back into the electrical box. You want to make sure that you align the two switch screws with the proper screw holes in the electrical box. Tighten the screws to make sure the switch is securely attached, and then replace the cover plate. Finally, if the dimmer switch uses a knob, press the knob firmly on the switch.

It is now time for the moment of truth: Return to the fuse box and flip on the breaker for the light circuit. You can then return to the room and test your dimmer to make sure everything is working correctly.

If you suspect a problem with your installation or you run into a problem, turn off the power at the circuit breaker and immediately get help from a professional electrician. For instance, if the breaker won't stay in the on position, you smell smoke, the cover plate for the switch is hot, or the lights won't work as you expect—all these are signs that you may need some help. Always remember that safety comes first!

Once your dimmer switch is replaced, it should work correctly and reliably for years to come.

Author Bio

Allen Wyatt

With more than 50 non-fiction books and numerous magazine articles to his credit, Allen Wyatt is an internationally recognized author. He is president of Sharon Parq Associates, a computer and publishing services company. ...


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What is 7 - 6?

2014-01-29 12:11:17

John Newell

My problem is how to get the knob back on the stem. When I push it on, the stem slides back into the switch housing and won't go on. I can't get it on from the back either.

I don't want to replace the switch since there's nothing else wrong with it.

When I try to submit this, it doesn't go anywhere and I get a message that says Flood Detected. ????

2014-01-29 12:09:41

John Newell

My problem is how to get the knob back on the stem. When I push it on, the stem slides back into the switch housing and won't go on. I can't get it on from the back either.

I don't want to replace the switch since there's nothing else wrong with it.

2013-12-31 07:58:33


I have a dimmer switch that works well, but the cap has fallen off. I have not been able to find a cap to replace it. At Home Depot, the salesmen said that they don't make that style any longer (one side of the extension it covers is flat) and that I'd have to buy a new dimmer switch. Where can I get a cap for my dimmer.

2013-01-17 23:19:42


Thank you!

2013-01-16 08:02:43


It probably isn't dangerous, but it is still drawing power. It wouldn't hurt to have an electrician look at it to determine if something is amiss with the wiring for the switch.

2013-01-15 17:58:40


I had a push on/off type dimmer installed for the chandelier in my kitchen. While the knob turns to brighten or dim the light, it does not push on or off. Although it dims to no light, I am thinking it is still on and drawing electricity because it techically isn't off. It also has a low hum. Do I need to have an electrician look at it? Is it dangerous?