I'm replacing a light switch in my house that has some very old wiring. When I removed the old switch I found that there are two hot wires, and one of them was joined with neutral – so on one end of the switch you had hot, and on the other end, neutral and the other hot wire joined together on the same terminal. To be clear I'm not basing this on color – I tested with a non-contact voltage meter.

I'm showing the wires labeled below, and how they were found connected to the old switch. #1 is neutral (or at least my meter indicates no voltage, and #2 and #3 both indicate that they are hot).

old wiring

old light switch

Inside the box, it seems these wires are coming in from three different pieces of conduit. It's hard to see in the picture below, but there is conduit coming in from the top, the right side, and the bottom. #1 comes in from the top, #2 comes in from the bottom, and #3 comes in from the right. There also seems to have been some splicing done in the past, there's something wrapped in electrical tape.

scary junction box

If my new switch was straight forward I guess I'd just put the wiring back the way I found it, but it's a little more complicated – it's a combo switch/outlet, and I want to wire it in the config that allows them to operate indipendently. Here are the two options they give for that setup:

wiring diagram for Eaton combo outlet / switch

So – how should I wire this in a way that won't mess up the existing daisy chain nonsense in the house? I.e. Where do I put the extra hot wire that was found originally joined with neutral?

  • 3
    Connecting a hot and a neutral together as you said will result in a short, tripping the breaker/fuse. You might have a switch loop that uses the white wire as a switched hot. With two wires(hot and white) maybe controls two lights. A picture of how the old switch is wired will help, showing all the wires in the box.
    – crip659
    Nov 19, 2022 at 16:53
  • @crip659 added labeled pictures. Also – this switch definitely only controls one light FYI
    – dongle
    Nov 19, 2022 at 17:01
  • 3
    If you call #1 "neutral" because it measures 0V, that may be wrong. For example it may be that #2 is your hot supply, and #1 supplies hot to something else. When it's disconnected it will measure 0V. Also, when you measure volts, you measure between two places. If you aren't sure where neutral is, what TWO places are you measuring BETWEEN in each of your three measurements? Also, can you post a picture like the first one with the inside of the box well lit? The wiring here is strange no matter how you look at it.
    – jay613
    Nov 19, 2022 at 17:10
  • 4
    Some advice unrelated to the question: the insulation on these old wires is brittle and you don't have much wire to work with. Minimize your handling of it. I like in these situations to use Wago 221s to attach the old wires to 8 inch pieces of stranded. This avoids twisting/untwisting the old wires ever again. Wrap them in tape as best you can, push them neatly to the back of the box and leave the stranded pigtails dangling. Then you work with those and never touch the brittle wires again.
    – jay613
    Nov 19, 2022 at 17:15
  • @jay613 added another pic and more info above. I was testing with a non-contact voltage meter, not a multimeter, which I understand can have false positives. Great advice on adding new wire to the end. In other places in the house that I've had to touch I added heat-shrink to the ends, but your advice is even better.
    – dongle
    Nov 19, 2022 at 17:33

2 Answers 2


Based on the question and comments:

I believe #1 is switched hot, #2 and #3 are hot supply and hot feed to somewhere else (I don't know which is which) and I believe the three taped wires are neutrals.

You may not have room in the box for what follows, but for what it's worth:

  • Test there is ground. The metal box should supply ground, hopefully through the FMC. That's not guaranteed and in fact unlikely. If not, get a combo light switch / GFCI receptacle. But .... that will leave you even less room in the box.
  • Replace the tape with a Wago 221-415 and add an 8 inch piece of white stranded #14 wire.
  • Put #1 and #2 together in a Wago 221-413 with an 8 inch piece of black stranded wire.
  • Put #3 in a Wago 221-412 with an 8 inch piece of red (or black marked with tape) stranded wire.
  • Connect your new black wire to a black screw, your new white wire to the silver screw, and your new red wire to the brass screw.

First, a caution about expectations. Switches do not use neutral, and many switches do not have neutral which means they cannot be tapped for power for outlets or onward circuits. So generally don't look at a switch and "expect" to tap power from there. It often won't work out. "Where do I get a neutral for my smart switch" is our #1 switch question and the answers usually are not pretty.

Now let's talk about those "unrelated" wires. Like I said, switches don't use neutral, so one guess what those wires are lol. So they seem to annoy you, but they actually make your project possible. "Thanks, fate!"

If you've googled common switch diagrams, you have "power to the switch" with an asterisk: Power (always-hot, that is) also continues PAST the switch, PAST the light and onward to other points of use. (or possibly the reverse; power may come from the light's direction and continue past the switch to other points of use; either way it won't affect the wiring.) So now we have the definition of all these wires, and a preferred color scheme.

  • 1 and 2, tied together, are always-hot coming from the supply and onward to other points of use (pref. black).
  • 3 is switched-hot to the lamp. (pref. red).
  • The two little wires in the back are neutral (mandatory white or gray).

Your new switch will have 3 terminals: Always-hot (common; do not separate), switched-hot, and neutral (silver screw).

Code requires that each wire have 6" beyond the end of the pipe and 3" beyond the surface of the wall. You will need to use splices to extend some of these wires. I recommend using #12 THHN wires of appropriate colors (any better hardware store, i.e. not big-box, cheerfully sells those for a quarter a foot). I personally prefer stranded, however stranded is forbidden in backstabs and requires skill on side screws (if it mashes into a mess that is wrong). If you buy better quality devices they use "Screw-and-clamp" which wires in the back but clamps down with the screw (torque HARD or to the stated spec). That said, I recommend solid wire for novices as it's just easier to work with.

Note that you need to establish that this location has proper grounding. If it doesn't, you will need to use a GFCI outlet, which they do make in that switch+outlet style. The switch will have 2 black pigtail wires; mark one RED. Here's the important thing in that case: Do NOT use the "Load" terminals at all or this configuration will be very messy. Don't even peel the warning tape! Read the instructions for how to connect 2 wires under 1 screw (the screw-and-clamp scheme I mentioned) and pile everything on LINE.

You can also use a GFCI breaker, outlet or deadfront between panel and this location, to protect the whole downline circuit - in that case you would use Load. However having a light on GFCI is not great - you trip the GFCI and now you are in the dark holding a hot curler, soldering iron, or fingers 3 inches from a still-spinning saw blade. No fun. Lights on GFCI are only required if they are inside shower stalls.

  • "Where do I get a neutral for my smart switch" is our #1 switch question and the answers usually are not pretty. Is diy.stackexchange.com/a/249909/11557 what you are referring to? I would love to see a definitive/summary question and answers - a search did not show much except your (very good BTW) answer
    – WoJ
    Nov 21, 2022 at 11:13
  • @WoJ A canonical might have issues because people have different situations - wiring method, fan+light, etc. Nov 21, 2022 at 18:50

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