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I am replacing a ceiling light fixture. I thought about replacing switch at same time, but didn't. It is one light fixture on one switch using a red, black, white and ground cable.

The switch is connected to the black and red wires, white is capped off in this box.

I attached the light fixture to the white and red and ground. I was pretty sure the black was capped off in the fixtures box.

The light won't turn off - is it possible that I should cap off the red and use the white and black for thew fixture?

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Wire color isn't a certainty, particularly with switched power. You need to be certain of how it was wired before and use the same configuration. Without that, you need to disconnect and use test equipment (non-contact tester, multimeter) to determine the neutral, hot line, which hot goes to the switch, and which hot is switched. A common convention would be black as always hot and red is a switched hot, but you need to test to be sure.

Once you have identified the wires, the light fixture will be connected to the neutral and switched hot. The hot from the line needs to go through the switch to become the switched hot. And neutrals should all be connected together.

  • Thank you. The only other thing I would ask is does it matter if at the switch red is on top and black at the bottom or vise versa? – Hankey Dec 17 '15 at 20:26
  • On a basic switch, it does not. Only with a smart switch that needs a neutral connection and powers something like a motion detector or timer built into the switch. These switches will have labeled inputs. The basic switches simply open and close the connection between the two wires, so top and bottom are interchangeable. – BMitch Dec 17 '15 at 20:28
  • Thanks, that's what I thought, but thought I'd ask anyways. I was surprised that the light stayed on when I was pretty sure I had just replaced everything as it was originally. – Hankey Dec 17 '15 at 20:48
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    The light staying on would indicate you've either confused or connected the hot from the line with the switched hot. So something isn't connected as it was before. – BMitch Dec 17 '15 at 20:53

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