We have a wall switch that does nothing in our new house. We think it’s for a ceiling fan that is not installed.
My old house had so many electrical issues it wasn’t funny - it was scary! One wall switch did nothing. Some of the time. Occasionally we would discover its use as an outlet turner-onner. Then when we WANTED it to work, it would quit for whatever reason.
An attic fan which may or may not still work?
We had a switch like this in our house, but we’d put it in ourselves and we finally got an electrician to crawl up into the attic and do what had to be done to install the fan and direct another switch to an outlet. It was a case of the best tool for the job being our checkbook!
That’s something we hadn’t considered - I’ll mention it to my daughter.
SIL and his brother figured out some of the switches and plugs in his “man cave” room, so he knows what they need to do. I’m guessing once they’re moved in over Labor Day weekend, they’ll go about figuring it all out. Such an adventure ahead! 
I had stuff like that in my house, too. The flourescent lights in my garage only worked intermittently, so I had an electrician look at them. It turned out they were installed by the previous owner by wiring them to a lamp cord which was plugged into one of those light socket adapters which was screwed into the socket above the washer/dryer, which was controlled by the light switch and apparently was the only light source in the garage originally. I had the electricians wire them properly.
When I bought the condo, we had a finished basement, fully carpeted, with a bar.
Did I say anything about electrical outlets? Nope. How the place got a CO I will never know. It’s telling that the building inspector did time a few years later.
Do you know whether the switch has power?
One thing that could help you figure it out is a chirper, like this one:
It tells you whether there’s AC voltage without having to make contact with the source. It’s called a “chirper” because it makes a chirping sound when it detects voltage. The one I linked to has adjustable sensitivity, so you can detect voltage through walls if you set it high enough. You might be able to use it to trace the wiring.
In any case, a chirper is a good thing to have. You can use it to tell whether you have power at an outlet, a light fixture, a switch, etc.
John Caldwell cartoon (quote inexact from memory), three switches, third one with a big toilet-plunger type suction cup near it. Homeowner instructing baby-sitter: “This turns on the room lights, this is the porch light, and this one will suck the face right off your skull. Dinner’s in the fridge, we’ll be home by eleven.”
Our family room has a 3-switch panel.
One is the master switch for the ceiling fan; the place did not have a ceiling fan when we moved in, but it was wired for it. We got a fan that had a remote, that slides into a little bracket covering that switch.
The second switch controls the lights over the fireplace.
The third switch controls… um, we’ve actually never figured it out. We’ve checked all the outlets in the room, and never found one that was controlled by it.
In our kitchen, there are three sets of lights. The ones directly over the sink, which are controlled by a 2-switch panel to the left of the sink. The other switch there controls the garbage disposal. Not confusing at all.
The light over the table is controlled by one switch on a 2-switch panel in the entry from the hallway to the kitchen. The other switch there controls the lights over the rest of the kitchen.
Each of those lights has other switches: the main ceiling lights can be controlled by a switch by the 2 steps into the family room, as well as a switch going into the dining room. The table light can also be controlled by a switch near the table.
Every now and then, all the switches will be down - and one of the sets of lights will still be on. Baffling.
There’s one “phantom” switch in our master bedroom closet. We think it’s for a light in the attic space - which has access only from that closet. I don’t know why the hell builders did that sort of thing - you simply can’t get into the attic without either emptying the closet or risking ruining all the clothes. Our last house was the same. The house I grew up in was the same. Builders are insane. One of these days we’ll put in pull-down stairs in the hallway like we did at the last place.
I have a very old home with sport wiring. So I added to it
Rather than move the switch in the kitchen for the VERY DANGEROUS Insinkerator next to the sink–because of electric code–I left the switch where it was, 6 feet away in a 4 gang switch bank with the insinkerator switch in white and the rest in black. When I sell it, my plan is to replace that switch with a red safety switch and cap it with a clear safety cap. Let them figure it out. I gave them fair warning.
Little known fact: many fluorescent light fixtures with metal reflectors will not work properly if the reflector is not connected to earth ground. That’s because the starting current relies on capacitive coupling between the bulb and ground. More info here: Fluorescent Lamps, Ballasts, and Fixtures
If they haven’t moved in, yet, I would suggest they map out the circuit breaker panel. That is, make a list of every switch and outlet in every room, either number them or name of the room they are in (for example MBO1 could be outlet 1 in the master bedroom, or whatever system makes sense for them). Then, before they have the house filled with appliances, devices, and furniture, check to see which switches and outlets are controlled by each breaker. I keep my list in a spreadsheet on my computer, with a hardcopy inside the breaker panel. That way, they if they need to shut the power to a specific outlet or switch, or they lose power at an outlet or switch, they can know exaxtly which breaker to check, instead of playing the “is it still on?” game.
Great idea! We ended up making one in out old house, because the grouping that belonged to the breaker was bizarre.
My house doesn’t have any mystery switches, but it did(!) have lots of electrical WTFs. Half of the wiring is copper and half is aluminum. It was built in 1968, and I’m sure sections are wired in whatever spool the electrician happened to grab off the truck that day. It isn’t circuit by circuit. I had to open every single outlet and switch to see if it needed aluminum remediation. Some outlets have copper coming into them, and aluminum going out.
One bedroom did not have any working ground. The power ran through an outlet in the other bedroom. The ground wire was not quite long enough to reach the outlet, so it was just left loose in the wall. I added a pigtail and got it connected.
Fortunately when the basement was completed at some later date it was done with all copper. Whoever did the work didn’t understand polarity, though. About half the outlets were connected backwards.
There is one mystery receptacle. There is an outlet on the wall inside a cabinet. It does not seem to work. I can’t take the cover off the outlet to investigate without removing a glued in shelf. It would be extremely convenient if the outlet was powered, so that I could put lights inside the cabinet.
The house we occupied for 47 years originally had no grounded outlets. Over the years we had a few installed. There was one switch in the LR that controlled nothing. Since all the other rooms in the house had ceiling lights, I guessed that the LR had had one and this switch had controlled it. I further guessed that if we wanted to install a ceiling fan, the wiring was there. Nope. When we were moving out a few days after settlement, the new owners were already tearing out the walls and ceilings and I got to look. No wiring there.
The house had new bedroom with an ensuite bathroom added a dozen or so years before we moved in. All the outlets were grounded at least. But the switch at the entry to the room turned on an overhead light and the bottom socket of every one of the outlets in the room. So each outlet–there were a half dozen–had only one usable socket. I can’t imagine what use a socket that was live only when that ceiling light was on could have had.
One of the light switches for an upstairs bedroom stopped working. There were three bedroom switches and three downstairs that controlled entry lights, outdoor light, and vestibule light and I decided to replace all 6 for some reason. So I bought six new light switches and on a bright summer afternoon turned off master circuit breaker and replaced all six. I was utterly astonished to discover that the 6 switches were all different and some looked like they went back to the 1910s. All different manufacturers and the like. The house was built in 1942, the middle of the war (from the Canadian perspective) and I can only assume that the builder could not buy new switches and had to scrounge them from wherever. I think that was an afternoon well spent. I just wish I had saved the 6 switches.
I would think that even in 1968 using the same type of conductor was required. I know it is definitely forbidden for different types of wire to be used in the same circuit. It sounds like someone wired their own house. A lot of mobile home fires were supposedly caused by aluminum wiring. I don’t believe it is used anymore.
Lots of things are required but not done… This house was one of the model homes for the neighborhood, so it was professionally built. The professionals may have been incompetent, cut corners, and had 3-beer lunches, but I’m sure the main floors were done by a builder. The finished basement was clearly done in the 70s, with the wood paneling and wet bar. The homeowner (a petroleum engineer) was or hired a competent carpenter, but a poor electrician.
I’m not sure when the patio was covered, but that seems to have been done properly. No weird electrical issues and all copper wires. I’m sure an electrician was brought in for that, because it looks like the old main panel in the basement was turned into a sub-panel for the new panel on the back of the house when the patio was done.
The risk of fire with unremediated aluminum wire is something like 40 times that of copper wire. Remediating with CO/ALR receptacles and pig tails, as necessary, drops it to just 5 times the risk.
I’ve got two of them in my living room, I’ve put a light into every outlet and switched them on and off but nothing happens. Weirdly, one of them is by the back door, and you’d think it goes to the light outside of the back door, but that switch is actually in the dining room.
I have a strange urge to connect an unseen tape recorder to an “unknown” switch:
“Thank you for pressing the self destruct button. The house will destruct in 5…4…3…”
Have you tried flipping the switch to the “On” position on a darkish cloudy overcast night? Perhaps it turns on the Batsignal.
Umm…
So what do the Goths (Gothamites?) do to call for the Dark Knight on a clear cloudless night?
I’ll paraphrase an old Readers Digest entry in their Humor In Uniform section:
A friend of mine was a firefighter and encouraged me to visited him some day for a tour of the station. I happened to stop by when he was in the middle of a poker game. He started showing me around and when we got to the garage his turn came up so he told me to wait, stay off the trucks, and not touch anything. So I admired (but didn’t touch) the trucks and looked around the garage at the cleaning equipment and the perfectly-labeled supply cabinets. And then I came to a big blue button without a label. My friend had been gone for quite a while and I figured I’d found something like a call button for walk-ins who needed a bandaid or something and figured I’d remind my friend that I was waiting by pushing the button.
Nothing happened.
I waited about two minutes and pushed it again, getting the same lack of results.
Just as I was about to push the button again, my friend came out and said, “What are you doing? I told you not to touch anything.”
I shrugged, looked helpless, and pretended innocence, but he noticed I was standing by that blue button.
My friend pointed to the roll-up doors for the garage and said, “I glanced out and saw the traffic. That button turns all the intersection lights red so nobodyi’s in our way when we get rolling!”
There’s a switch in my living room that currently does nothing. It’s right by the sliding glass door next to the switch that turns on a flood light that is pointed out over the pool. The dead switch used to turn on the little lights on the deck on the other side of the pool, but when a tree fell down a couple summers ago, the trunk smashed a littl junction box nearby that included the wiring that feeds the deck lights. And, quite frankly, we haven’t missed the deck lights so it hasn’t been an urgent matter to get that line fixed. So I know what the switch is for and what it’s not doing and just have to hope I fix that line before I die (or we move out, whichever is sooner). Until then, it’s a dead and only-known-to-me switch.
–G!