Hello, new to the forum, I've lurked here before but this problem is so strange I thought I should make an account. I've worked on plenty of receptacles but never a light switch. I only happened to check this switch by chance because I was removing the switch which is right next to it for the outdoor light and saw it had no back cover on (so it was previously worked on) it so I decided to investigate real quick and I'm glad I did.

The light switch and fixture works and has for 13 years, but something is clearly wrong. First off it is a mobile home and uses those SCDs (self contained devices) where the wires are pressed into these spring tension blades which cut through the insulation and clamp the underlying copper.
I used a multi meter on the light switch on the blades where they make contact with the copper, and I am going to give you the results of checking each combination both with the light switch off and with the light switch on.

With the light switch off
Neutral-ground - 120v
Neutral-hot - 103v
Hot-ground - 0v

With the light switch on
Neutral-ground -120v
Neutral-hot - 0v
Hot-ground -120v

So there you go. Anyone have any ideas as to what could be causing this? Again, it works fine somehow and it's been like this for as long as I have been here, but it's not right. Thanks ahead.

 

These readings are indicating an open neutral somewhere.

 

I have updates, sorry this will be long winded. Picture related, the switch pertaining to this thread is the one on the left. I went and looked at it again and noticed something I'm not sure how I missed. There is one wire going to it, so one hot, one neutral, and one ground. The neutral was looped around connecting on the neutral side and the hot side. I'm not mistaken about this am I? Picture on the right is from the switch I removed earlier that was for the outdoor light. The left switch this thread is about just stopped working as well, I pulled it back out and as I was measuring voltages again slight bumps made the light flicker and it quit entirely, acted like it had a loose connection but removing the wires from the blades says otherwise. I removed it and checked the voltages to just the wires now.

Hot-Neutral - about 105v (and it was hard to get a consistent reading)
Neutral-Ground - 120v
Hot-Ground - 0v

So what in the world exactly? It's disconnected right now, hot and neutrals have wire nuts on them and it's tucked into the hole where the light switch was. It's very late now, time just zoomed by.

 

No pictures.
how-insert-pictures
Are you saying there is only a black and white wire connected to the switch? If that is true then you do not have a neutral. The white is being used as a hot.

What exactly is the problem you are experiencing?

 

More updates and sorry, here is the picture. Again, the switch this thread is about is on the left, the one I first removed is on the right. They are both removed now though.

I wasn't having a problem with this switch (I thought). Not sure if this is related to the switch this thread is about but here it goes. The switch right next to it was for an outdoor light that is never used and I thought was just disconnected at the switch. I removed the outdoor light (was going to put a solar there instead). Behind it were two wires going to it, the grounds were twisted with a wire nut, a hot and neutral were twisted (white must be a hot so we will say black/white from now on), and the remaining hot and neutral were not twisted and went to the outdoor light. Since it was disconnected from the switch the only live wire was the black wire which was part of the black/white twist. I untwisted the black/white outdoor wire and put a wire nut on them. This killed the wire which once fed the outdoor light switch. Whether those wires are twisted or not has no effect on the switch this thread is about though, I got the same readings either way. But, I think it's now pertinent since it shows whoever was previously here did some strange things and maybe didn't know the difference between black and white.

I made this thread after discovering strange readings on the indoor light switch that this thread is about. The light worked fine until I messed with it too much. It blinked out, behaved as if it had a loose connection when I had it pulled out of the wall, fizzled and the light went out, no power went to the terminals in the socket after that so it went out on the switch side. If it was a normal wire with normal readings it would be no big deal and I'd just replace the switch. So now it's just a wire, and it doesn't appear I should be using this wire because the readings are all wrong.

 

So if the white is being used as a hot, what's the black? Because black to ground is giving me 0v. And what about black-white being a bit under 120v (averages 100-105v)? I took a single pole and wired it up as if the white and black were both regular hots, wired the ground as well, and switched it on, worked as you'd expect because it's been working for an unknown amount of years (unsure when it was done like this). I took it back off, don't want to wire it like this unless it's safe.
I've been trying to read up, is this something called a "switch loop" by any chance? Would that explain the strange readings when I measure white to black? By the way, the black wire does not set off a tester, so no way it's a hot.

 

Your left picture is a switch loop. The power comes to the switch on white and gets carried back on the black. If this switch controls a receptacle..... you need to check at that receptacle. The diagram below shows a light but a receptacle would work the same way.

 

Okay, it's starting to make sense. It looks like there were two switch loops then. One for the indoor light and one for the outdoor. I just went outside where the outdoor light was and temporarily wire nutted the black and white like they previously were. As you'd expect the wire coming in (that was once hooked to the switch on the right) had a hot which was white. Unlike the indoor wire, the outdoor wire was black-white -0v. But this would be because the other white and black weren't connecting to anything (light is disconnected). The indoor wire gives me 100v-105v from white to black, but this is because the multi meter is completing a circuit where the light is. Somehow it's losing 15v-20v, know why that might be?
This switch does not control an outlet but a light, it's worked for at least 13 years, I only just discovered it was a switch loop and didn't know what a switch loop was until today. So it looks like the indoor light should be safe to hook back to a new switch unless that 15v-20v loss between black and white means anything.

I don't recall the outdoor light ever working in 13 years, a long time ago two people tried to help with it and just said it wasn't right. I knew a lot less about maintaining or fixing things and didn't seek to learn like I do now. Strange that it was using two wires then, top and bottom. The hot side (white) was where the neutral traditionally would be. And you would switch the light on and off using the black. Would this have been possible? The switch only had a bottom wire going to it when I pulled it out, the top was cut off about one foot from the top of the switch, so the return just wasn't hooked to anything at all I guess. Either that or someone just didn't know what they were doing, but there wasn't much evidence of a DIYer pressing those wires into the blades, seems like it would have been near impossible to do by hand without the special tool so there should have been damage somewhere. My head hurts, wish I just knew what happened. Outdoor light isn't going to be used anyway, the hot is wire nutted with plenty of electrical tape to boot.

Sorry for rambling about the outdoor light/switch when this thread was about the indoor switch, probably getting confusing reading this post. I just figured it's now pertinent. I thought there was some unholy splicing somewhere in the ceiling.