I have an interior light switch that turns on/off an exterior light. That worked fine for many years. Then I had a motion sensor added outside on the roof ten feet away on the second floor. It is connected to the outside porch light by 14 guage wire to the said switch inside the front door. It’s been working for the past 25 years. You could walk up to our house at night or flip the inside switch 3 times and the porch light would come on. It stopped working.

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I thought if I completely disconnected the motion sensor and put wire nuts on the line (14 gauge white and back wire) then I could manually turn on or off the porch light.

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The porch light doesn't work. I put new switch inside but the porch light will not work.

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I took down and checked the porch light by attaching a plug to the light wires and when I plugged it in the porch light worked. I then connected a outlet to the wires that go to the porch light to test the plug to make sure it was active and I plugged a light to the outlet. The light wouldn't work and the wire to the outlet no longer had current. When I unplugged the light from the outlet, there was current back to the outlet.

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I can’t go into the attic to see how the motion sensor is wired or change the wiring due to tight space and tons of insulation.

At this point I’m reaching out to this community to try to solve the three following questions:

  1. (Most important) How can I wire the existing setup so that I can go back to what I had before the motion sensor was wired - where I can turn on/off the light switch?
  2. When the electrician added the motion sensor did it effectively create a loop, so that now the motion sensor wires are capped off and not connected to anything the light switch will never work?
  3. Picture 6 shows an outside box that goes to the light fixture. I was wondering why there is a white and black wire connected together by a yellow wire nut. They are both hot. Why? Also, why are the two switches connected together inside the box?
  • #3 is usually a switch loop(old style) where the white is used as hot to a switch. White/neutral is not used for simple switches so it saved copper. #2 the motion sensor was probably connected between the switch hot and the light's switch hot. Will need to find/determine those two wires and connect them. Knowing how the motion sensor was wired up will help.
    – crip659
    Commented Dec 13, 2023 at 14:04
  • 2
    Please post the pictures you took of how everything was wired before you disconnected/changed anything. Commented Dec 13, 2023 at 14:32

1 Answer 1


You needed to connect (the wires that were connected to) the motion sensor black and red wires at the motion sensor location (or rewire the light, but if you might replace the motion sensor that's the easy/quick fix.) That's what the motion sensor was doing when it worked and turned on the light. Though it would appear that the motion sensor was improperly wired with ground as neutral, based on the wires on it, and the wires from its box. Unfortunately you have not posted any "as wired before you changed them" pictures.

That would be with all the other connections where you had them before. Since you've rearranged them, and the wiring was improper, perhaps rewiring the light is the better option.

Black and white connected together are a sign of an old-style (pre-NEC2011 adoption) switch loop. That white wire should be but often is not marked with black or red to indicate that it is a hot white. Oddly it seems to be in one photo, and then not in another. Apparently where that was going to was the motion sensor, as we don't see a hot white at the actual switch.

Given the improper wiring of the motion sensor, disconnecting the cable with the hot white entirely and connecting the light ONLY to the cable with the black that was connected to the hot white SHOULD be the correct arrangement, as best I can make out from your description and pictures.

The two switches are wired together in the box where constant-hot connects to them. Switched hot goes from the other terminal of the switch. They do not appear to be arranged in a pre-2011 switch loop.

  • So literally connect the black/red wires together to finish the loop between that and the light switch?
    – Zach Smith
    Commented Dec 13, 2023 at 14:35
  • When you started, yes. Now, perhaps not. See my edit. And not the red-black in your switch box - the black white that were going to the red black of the sensor. But the sensor was improperly wired with ground as neutral, so disconnecting that cable would be better, with everything opened up.
    – Ecnerwal
    Commented Dec 13, 2023 at 14:38

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