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My old home has a mixture of knob and tube, 2-wire, and 3-wire (w/ ground). I replaced an incandescent floodlight with a motion sensing, LED light. The circuit also has another switch in the garage, a garage light, and another incandescent flood flight. Both switches control all three sets of lights. My issue is the LED lights don’t come on at all. I checked that electricity is flowing through the device with a non-contact voltage detector. I used a known good light when I thought my new one was a lemon. Both lights come on when put on a different circuit. Could my old 2-wire system be the cause? Could there be a low voltage situation? I’m unsure about what’s going on as I’m not an electrician.

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    Are you testing during daylight? Did you know motion sensors also have light sensors to avoid turning on in daylight? Does the area get a lot of nighttime ambient light from skyglow, street lighting, neighbor lights etc.? If you tape the switch to stay on, and give it 24 hours, does it start working normally? (it may need to calibrate to day/night lux levels at that location). – Harper - Reinstate Monica Feb 23 '20 at 20:43
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    Also, is the switch smart, lighted, dimmer, motion sensor, anything weirder than a plain old switch? – Harper - Reinstate Monica Feb 23 '20 at 20:46
  • a Non contact meter is not reliable method for verification of true voltage it could be phantom voltage, with that said I would want to verify power with another fixture. In my experience k&t rarely fail because of the number of wraps (pre wirenuts) however you could have an open neutral broken wire at the fixture so there is not a complete path for power on your new fixture. – Ed Beal Feb 24 '20 at 15:50

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