I've searched round the forum and web, and found others asking similar, but slightly different questions.

I have a security light currently wired to a constant circuit so that it trips whenever there is motion. Which is a good thing.

However, I also want the light to turn on and stay on, when I turn on two other light in the front of the house that are on a switch.

I know that these lights generally have a flicker over-ride that would work, if I were to hook them up to the same switched circuit the other lights are on.

But how can I also wire the light to a constant source as well?

Please excuse me if I am lacking the correct terminology.

Thanks in advance.


You might be able to accomplish this by replacing the existing front light switch with a three way (SPDT) switch and running a new 3-wire plus ground cable from that switch to the back lights.

It's basically a three way switch with a two way switch in series on one leg, where the motion detector is the two way switch.

This would only work if the motion detector in the back is OK with this type of connection. You'd have to consult with the manufacturer of the motion detector about that. It's never come up for me so I have no idea if that runs afoul of the listing of those devices.

At the back light, splice the black on the light, the red from the new cable, and the red from the motion detector. Splice the black from the new cable to the black from the motion detector. Splice all three whites. Ground wires as usual.

In the switch box, connect the black going to the front lights and the red from the new cable to the "up" position traveler terminal on the SPDT switch with a red pigtail. Connect the "down" position traveler terminal on the SPDT switch to the black wire from the new cable. Connect the common terminal on the SPDT switch to the black wire feeding the switch box. Splice all three whites. Ground wires as usual.

When the three way switch is on, there will be 120V on the motion detector's red wire and 0V on the black. That is not how it is usually wired, and may not be OK for the device, that's why I mention checking with the manufacturer above.


I gave this some more thought because I think it's an interesting problem / exercise. I thought of another alternative that may or may not be worth the trouble.

If you can't find a motion detector that's manufacturer approved / listed for parallel wiring, you could sidestep that by using a DPDT switch rather than a SPDT switch. The second pole would be to disconnect the motion detector from the light and the parallel power when the front lights are turned on. You'd have to run an additional 14/2 or 12/2 from the front switch to the light. You probably see where I'm going with this but I'd have to make a sketch to explain it any better.

That may be more trouble that you'd want to bother with. Complicated is never good. You may have to install a bigger switch box up front and / or a bigger box / second box in the back.

  • These are existing lights. I think they are these: heath-zenith.com/products/par-300w-150-sen-gr?taxon_id=4 and the instructions only address a very basic wiring scenario. But what you say makes sense... – JSM Nov 12 '15 at 17:41
  • Unfortunately, these instructions don't work in the OPs case, as it appears the sensor on his security light is integral to the fixture. – ThreePhaseEel Nov 12 '15 at 23:47
  • The light and sensor are currently combined, yes. However, if by installing a separate sensor and light, I can solve this issue, I will probably do that. Can one of you confirm that the above solution would work with separate components? – JSM Nov 16 '15 at 20:12
  • You'd still need to confirm with the manufacturer that the standalone sensor would be OK wired in parallel, but I would think you can find one that is. Might be expensive though - a good quality sensor is pretty expensive, more than a whole fixture / sensor set at the big box stores. – batsplatsterson Nov 16 '15 at 22:22
  • I was thinking about this and you could actually sidestep the issue of whether it's OK to wire the sensor in parallel with a DPDT swtich, I am going to edit my answer with details. – batsplatsterson Nov 18 '15 at 11:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.