How can I figure out what mystery wall switches might do?

Question

I have a two-story house with blown-in insulation in the attic. There are at least four wall switches in my house (some on the ground floor, some upstairs) that seem to serve no discernible function. I have asked the previous owners of the house and the owners before that, but none of them know the function of these switches. The first family to occupy the house is no longer alive.

What techniques might I use to figure out what these mystery wall switches are for? I've tried all the outlets, and they don't seem to turn any of them on and off, and I can't find any mounted lights controlled by the switches.

Answer 1

First thing I'd check is if the switch is even connected to any wires. You can probably check this just by removing the face plate.

You already checked the receptacles, but did you check both the top and bottom outlet? Sometimes a switch will only control one part of the outlet. In this case, the metal tab connecting both hot terminals is broken so that the top and bottom outlets can be individually powered (and switched).

The next step is to look at the wiring of the switch. First turn off the circuit breaker and test again with a non-contact tester (if you don't know what the switches do, then it could have more than 1 circuit in the box - just to be safe). Remove the switch and take note of the switch type - is it a single pole switch or 3-way switch? (If its a 3-way switch then the color of the traveler might be helpful in finding what it controls.) Is the line (from the circuit breaker) in this box?

If a visual inspection doesn't give you any clues then you need to trace the circuit. This is usually done with the power off using a circuit tracer:

A telecom probe/tracer can also be used in many cases. You hook the tone generator up to the wires at the switch, and then you use the probe to follow the wires through the wall. With any luck you will find your way to a ceiling or wall box. Depending how badly you want to know, you might need to open the wall (or use a scope) at some point to help trace the wire. More expensive versions of this tool exist that might be needed to find really sneaky wires.

It's not unheard of to find out that a previous owner dry walled over an electrical box, so keep this in mind as a possibility.

And if you just can't sleep at night without know where it goes, you could always x-ray your house as a last resort.

_{(source: tomcomunicacao.com.br)}

(The above image is by photographer Nick Veasey. While this photo was stitched together, there are companies that x-ray buildings )

Answer 2

I had one circuit in my house where the outlets were originally wired as split outlets - the top of all of them was switched, and the bottom was always on. Then, the owner replaced one of the outlets, but they didn't know what they were doing and forgot to break the tab on the outlet connecting the two hot sides together, which made them all on all the time. Breaking the tab on that outlet fixed the issue.

Answer 3

Estimated cost: under $50
Estimated time: under 30 minutes

I had a similar problem in an upstairs bedroom. I found the answer in several different sections across different forums. Take all safety precautions- at least turn off the power to the room you are working in (after step 1).

Step 1- determine if the switch has electricity (you can buy a cheap electrical tester at the hardware store for $10 to $30) (Now you would want to turn off the power and take any other necessary safety precautions)

Step 2- Open up the switch by removing the switch plate
Step 3- determine if there is a red wire. If so...
Step 4- open each outlet in the room to determine if any of them have a red wire too. If so, that is the outlet connected to the switch.
Step 5- remove the outlet from the wall by unscrewing both screws holding it in place
Step 6- locate the "outlet tab" between two screws on the side of the outlet (below is a picture) or you can search for images of "outlet tab"
Step 7- using a pair of pliers (needle noise would be easiest) wiggle that tab back and forth until it breaks
Step 8- ensure all wires are connected properly
Step 9- put all components back in the wall
Step 10- test the switch (with power restored)

Now one plug should be hot all the time and one should be controlled by the wall switch.

If that did not fix the problem you may want to consider replacing the switch as well. If that still does not work you most likely need to have an electrician come out to ensure the wires are not interrupted somewhere between the switch and plug.

Answer 4

I'm a few years late to this thread, but I was looking for that circuit tracer device.

One possibility that was not addressed here is that some houses are planned to have a ceiling fan/light combo installed and so two wall switches are installed during the build. However, the fan might not be installed as planned - in one of my houses, they did not install a light in the fan, so I had a "mystery" switch. Also, a wireless fan controller could be installed, too, creating two such switches.

Another possibility is an outlet where you would not expect one. I've had three houses with decorative shelving from 8 to 12 feet off the ground, each having a switched outlet for the purpose of "mood" lights. I discovered the first of these after setting up a ladder to install garlands for Christmas, and was quite happy to see that I could plug them in.