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I tried installing a light fixture in a previously unused light box (so cannot use how previous light was wired as a baseline).

My light fixture has a black live wire, a white neutral wire and a green ground wire.

The box in the ceiling has 2 black wires twisted together, 2 white wire twisted together, a red wire and a bare copper wire.

I wired the black box wires to the fixture black wire, the whites to the white, the copper to the green and left the red wire alone.

When I turned the breaker back on, the light was on and flipping the switch did not turn it off.

I replaced the switch, but that did not do anything.

My best guess is I wired it wrong but I have no idea what the right configuration would be.

Edit: Connecting the black light wire to the red ceiling wire fixed the issue. Thank you!

Diagram of the wires as best as I can see

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    I am betting that if you turn off the breaker and take out the switch, you will find a black wire and a red wire. If so connect black light wire to red wire, and white to white. Report what you find before doing. – crip659 Jun 1 at 20:18
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    The Switch was connected to a black wire and a red wire. Huh, I'll try that. – Felix Jun 1 at 20:22
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    Just wondering how white wire is done at the switch? In your case it should probably have a wire nut on the end at the switch. – crip659 Jun 1 at 20:27
  • Well, that was from when I changed the switch to see if that was the problem, at the time I didn't poke around too much and just disconnected the 2 wires (1 black, 1 red) connected to the old switch and connected them to the new one. I didn't take out the white wires to see what they were attached to. – Felix Jun 1 at 20:31
  • You really only need two wires(plus ground) going to switch. One wire(white) is not needed and should be disconnected at both ends and have a wire nut placed on both ends. Most people would just a two wire cable(white and black) and put black tape/paint on white wire to show it was hot(switch hot). – crip659 Jun 1 at 20:50
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What I suspect you have (ignoring the grounds) is:

  • One cable coming in with hot (black) and neutral (white)
  • One cable coming in white hot (black), neutral (white) and switched hot (red).

The hots all connect together. Do not touch them.

The neutrals all connect together. Add your light's white = neutral to this bundle.

The switched hot connects to your light's black wire so that it is switched.

Colors, except green/ground and mostly white/neutral have no inherent meaning. But in standard cables, you will normally have black = hot and red = switched hot. (Except when you don't.)

Note that in the good 'ol days, a switch like this would have two wires in the box, not three. So you would have black and white but no neutral. New code requires neutral in the box, therefore /3 cable, therefore white = neutral, even if neutral isn't actually being used. When neutral isn't used, the white wire is capped in the switch box. But that is good because if you decide to add a smart switch, timer, etc. then you have neutral ready and waiting.

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    Re white wires follow the advice in this answer to connect the whites in the ceiling box and leave it capped in the switch box. There's a comment saying you should cap it at both ends. By following this answer, if you later want to install a fancier switch it'll be a five minute job. (EG, Smart switch, timer, night light, combo outlet, etc). – jay613 Jun 1 at 21:54

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