How To Find What A Light Switch Controls (Do This!)

Brigid Levi
by Brigid Levi

Every house seems to have that one light switch that controls nothing. I have several in my house. It can be quite frustrating, but fear not! There are a few ways to hunt down what your mystery switch controls.

Using a lamp as your tester, plug it into various outlets and flip the light switch until the lamp turns on. You can also use a wire tracer device to trace the live wire from the light switch to the circuit that controls it. Lastly, try opening all the outlet boxes in the room to see if there are any disconnected cables.

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The Lamp Method

This oldie but goodie is a simple, low-tech way to solve an annoying problem. Before you do anything, first check all the bulbs in the light fixtures to make sure they aren’t dead. If any are, turn the switches off and swap them out. Then, turn the switches back on to make sure all the bulbs are now working.

Once you’re sure the bulbs are good, shut all the light switches again. Get a small lamp that is easy to move from outlet to outlet. Make sure the lamp is turned on.

Then, plug it into various outlets, turning the switch on each time until the bulb lights. When that happens, you have found the outlet controlled by the mystery light switch! It’s important to shut the switch off each time you remove the plug so you don’t accidentally short out the bulb.

If you’ve plugged the lamp into every outlet in the room and the bulb stays unlit, you can move on to another method.

Tracing the Wire

If you can’t seem to find an outlet that works on the light switch, you can attempt to trace the wires going into the switch. Don’t worry—you won’t have to remove the walls! You can trace them physically if you have an attic or a basement. Or you can purchase a wire tracing device.

Using a Wire Tracer

A wire tracer is similar to a stud finder except for wires. The device consists of a transmitter, a probe, and an adaptor. There are models that require the cables you’re testing to be de-energized. Others allow you to trace live wires, though these tend to be more expensive.

Wire tracers can help you find wires behind walls. They can also locate the other end of a wire. Here’s how to use a wire tracer on a mystery light switch:

  • Attach one of the alligator clips to one of the wires going into the light switch.
  • Turn on the transmitter.
  • Move the probe along the walls of the room to trace the wire. As you get closer to the connected wire, the probe will either light up or make a sound, or both. When you’ve found the correct wire, the probe will make the loudest sound thus far.

Now, you’ve found the wire connected to the light switch. If it’s in the vicinity of an outlet, there’s a possibility the wire isn’t connected properly. This is especially true if you previously used the lamp method to no avail.

If you have a gas fireplace in the room (or know there used to be one), it’s possible this switch attaches to the optional fan at the bottom of the fireplace.

Finding the Right Wire Tracer

Should you choose to go this route to test your light switch, you want to find the best wire tracer for the job. You want to look for trusted brands like Ideal Industries or Klein Tools, both of which manufacture high-quality wire tracers.

You also want to pay attention to the wire tracer’s attributes. How good are the sensitivity adjustment, penetrating capacity, and transmitter power? Is it durable? And finally, it has to fit in your budget.

Checking the Outlet Wiring

Whether or not you use a wire tracer, you still have the option to check the wiring in each outlet. After removing the cover plates, check that all the surrounding wires are properly connected to the outlet.

It’s possible that an old wire may have gotten disconnected. This would cause an improper function of the light switch. If this is the case and you feel comfortable, reconnect the wires. The switch should then control the outlet.

Call an Electrician

When all else fails, call an electrician. They will be able to get to the bottom of the problem. You may have a wiring issue that can only be solved with the help of a professional.


Related Questions

What happens when you flip a light switch?

The light switch essentially opens and closes the circuit. When the switch is in the on position, the circuit is closed which allows the electricity to flow through the wires and power the fixture. When the switch is in the off position, the circuit is open and no power can be transmitted.


Does it matter which wire goes where on a light switch?

If you want the switch to function properly, then it does matter where you attach the wires. The hot white wire should come down from the ceiling. And the hot black wire should go up toward the ceiling.


What amp should a light switch be?

If you have one or two lights attached to one switch, a 15 amp is acceptable. Any more than two lights and you’ll need a 20 amp switch.

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Summing It Up

There are several testing methods available to find out what a light switch controls. The low-tech lamp method is tried and true, albeit time-consuming. For this one, remember to keep the switch off as you plug and unplug the lamp in different outlets.

You can also use a wire tracer to locate the wire attached to the switch. Although you may not necessarily be able to fix the issue, at least you’ll know where the wire is!

The last DIY option is to check the wiring in each outlet in the room to make sure everything is properly connected.

If none of these options work, call an electrician!

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Brigid Levi
Brigid Levi

Brigid Levi is a wife, mother, and freelance writer who enjoys a good DIY project and creating beautiful spaces within her home. From cleaning and organization hacks to home decor ideas, she loves helping people in their quest to turn a house into a home. Her hobbies include pretending to be Joanna Gaines while updating her home with her husband and performing in local theater productions.

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