enter image description hereI recently had a renovation complete with only the rough in work done for electrical. Due to the pandemic, its hard to get people to come by to finish the work. I am trying to install a single pole light switch for my laundry room, but i am confused by the layout of the wiring to the box. It seems there are four wires coming into the box - and i cant tell which to use to wire the switch.

Any help would be really appreciated, or an explanation. Thank you!


  • 1
    Oh hey, I see you posted a photo now :) Perfect!
    – J.Hirsch
    Apr 6, 2020 at 16:28
  • 1
    Guesses - P-IN is Power in, so that's going to be the hot wire that connects to the switch. Check and see if that wire is hot (check voltage between that wire and ground or a white neutral). The black and white wire that are connected shouldn't normally happen. I suspect this is the wire that goes up to the light and the ends have just been capped together to mark them. Using a continuity tester can show if these are the two wires that go up to the light. Take off that wire nut and see if those black and white wires are even stripped.
    – JPhi1618
    Apr 6, 2020 at 16:30
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    Did this use to be a 3-way switch? The black/white capped together would normally be to the light and back (a 'runner'), but typically good practice is to at least sharpie around the white wire or wrap a bit of black electrical tape on it. If "P-IN" is hot when the breaker is on, and everything else is not then something else is going on.
    – J.Hirsch
    Apr 6, 2020 at 16:32
  • Kinda odd that you accepted an answer without answering anyone's questions. Glad that helped, but it was pretty general advice.
    – JPhi1618
    Apr 6, 2020 at 19:14

1 Answer 1


Assuming US

...you didn't take a photo, did you?

Assuming you haven't mangled the old switch wires, take a photo of how they look and post it.

Typically (TYPICALLY!!!) you'll have a 'feeder' circuit- that'll be one set of black/white/copper coming in. You'll then have another black/white/copper going out (probably up, if it's a light, but that's because of the way walls work).

The 'feeder' circuit is going to be 'hot'. You have the power to the wall turned off right? You should also see a pigtail (wirenut) around one of the sets of wires- they should have been twisted together. The wire that went to the switch should have a bent curve around it. The feeder wire is bent (black) and goes to the lower portion of the switch. The lighting circuit black goes to the top of the switch. The two white wires get tied together via wire nut.

The copper wires get tied together and two little 'pig tails' come off of them- one goes to the metal box to 'ground' it and the other goes to the switch (green screw) to 'ground it'.

But please, post photos. These are ALL ASSUMPTIONS. And if you aren't sure or don't know, please don't. You can hurt yourself badly.

And if you have any other colored wires- red for instance, your circuit is more complicated.

Also, if the breaker is off, you can cap off the switch wires with a wire nut and turn the breaker back on temporarily- that'll tell you if there is any down-stream wiring that would make this more complicated.

If you really only have 4 wires coming in- black/white and black/white, then you have no grounds, and you follow the same thing as above but no grounding the outlet box. So you need to be doubly careful as if you energize the switch it won't necessarily fault out but could energize anyone touching it.

And if you don't have grounds and this is a bathroom, then you need a special breaker called an Arc-Fault / Ground-Fault Interrupter. They're expensive, but you should have that in there to protect you and your family.

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