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I originally had a ceiling light with a smoke detector in the ceiling. After removing it, I discovered two black, two white, two red and one ground wire in a single box.

When I turn on the switch, only one set of black and white is live (tested with a voltage pen). The two red are always live.

I tried to wire the new light to the set of black and white that will go live when the switch is on but the new light will not turn on when the light bulb is attached. Can someone help me understand this setup? Thanks.

  • A light with a smoke detector? As in an integrated unit? – isherwood Sep 25 at 13:47
  • Yes, it was fan+light+smoke detector of sorts. – James Li Sep 25 at 14:03
  • The live reds are a mystery. With modern smoke detectors they're simply a low-voltage interconnect, but I'm not sure why there would be two here. Please update your post with information about how the original fixture was connected. – isherwood Sep 25 at 14:05
  • I honestly do not remember how the original fixture was connected. I should've taken a picture when I removed it back then. – James Li Sep 25 at 14:14
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    I suggest getting yourself an inexpensive multi-meter and checking actual voltages. Whether the reds are line-level or low-voltage would be good to know. – isherwood Sep 25 at 14:28

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