Exterior dusk/dawn sensing lights all stopped at once

[bbp]

I bought my house in 2018. It was built in 1992 and has 2 sets of exterior lights, one set in the front yard and one in the back yard. Each set is controlled by a switch inside the house. Each switch is part of a box with 2 single-throw switches. The other switch in each box controls an interior light; both interior lights work fine. When the exterior lights worked, if the switch was thrown and it was past dusk, the exterior lights would be on. If the switch was not thrown OR it was light outside, the lights would not turn on.

One day, both front and back exterior lights would no longer turn on at dusk. No breaker flipped in the fuse box. Bulbs are fine. I've measured voltage across each switch at both boxes:
Front yard box
- exterior light switch: 0v when open/closed
- interior light switch: 12v, behaves as expected

Back yard box
- exterior light switch: 0v when open/closed
- interior light switch: 120v, behaves as expected

As you can see, both exterior light switches in 2 different boxes at completely opposite ends of the house have no voltage. I'm pretty handy but am not experienced with the various ways exterior lights can be wired and this one has me baffled. I'm hoping that someone one here who knows building conventions can help me figure out how this lighting circuit is configured. Some open questions I have are:

- Can both lights be on the same circuit even though voltage is 120 at the back switch and 12 at the front? Is it possible to step down the voltage after the breaker box?
- Could there be a separate, standalone light sensor that has gone bad? I've never noticed one around the exterior of the home nor seen any special switch or box in the garage.
- What are some places I can check in my garage and around the outside for exterior light sensors/boxes?

Thanks for reading

 

[Snoonyb]

Welcome.

Shut the breaker/s off that you have identified, control this/these light circuits, remove the cover and the switches to a position that the conductors are clearly visible, and post a photo of each.

Also describe how the exterior light fixtures are mounted and to what.

 

[bbp]

Thanks for responding, Snoonyb.
Here are pictures of the front fixtures/switches. Exterior switch on left, interior on right.



And backyard fixture/switches. Exterior switch on left, interior on right

 

[Jeff Handy]

Find the correct breakers for those switches and turn them OFF.
Some breakers look ON, but are actually set in the middle, after tripping.

They have to go fully to OFF, then back to ON.

If you can’t find the breakers, then do this to every breaker in the panel.
Unplug electronics like computers and tv first.

If this does not fix the problem, then turn off main power breaker.

Remove the switch wires from the back stab holes, you might have to insert a thin metal tool into the release hole next to each wire as you pull.
Back stab connections suck.

Put the wires where they belong, which is around the screw terminals.
Expose a little more wire if needed, about 3/4 inch total.
Loop the wire around the screw clockwise.
It does not matter which wire goes to which screw.
As long as they are single pole switches.

Check any wire nuts in the switch junction boxes, take apart and redo just to be sure.
Their can be more than one breaker feeding a box, so if you left main power on, be careful.

Often safer to do this work with main power off, during daylight.

Replacing the switches might not be a bad idea.

During this repair, leave the switches out of the boxes, as in your pics.

Easier to test and rewire with them like that.
Don’t touch any bare wire or screw connections.

Don’t let switches touch each other or the metal box.

Keep kids and pets away.

 

[Jeff Handy]

Your 12 volt reading might be for a switch or dimmer that controls a low voltage halogen light fixture.

 

[bbp]

Find the correct breakers for those switches and turn them OFF.
Some breakers look ON, but are actually set in the middle, after tripping.

They have to go fully to OFF, then back to ON.

If you can’t find the breakers, then do this to every breaker in the panel.
Unplug electronics like computers and tv first.

If this does not fix the problem, then turn off main power breaker.

Remove the switch wires from the back stab holes, you might have to insert a thin metal tool into the release hole next to each wire as you pull.
Back stab connections suck.

Put the wires where they belong, which is around the screw terminals.
Expose a little more wire if needed, about 3/4 inch total.
Loop the wire around the screw clockwise.
It does not matter which wire goes to which screw.
As long as they are single pole switches.

Check any wire nuts in the switch junction boxes, take apart and redo just to be sure.
Their can be more than one breaker feeding a box, so if you left main power on, be careful.

Often safer to do this work with main power off, during daylight.

Replacing the switches might not be a bad idea.

During this repair, leave the switches out of the boxes, as in your pics.

Easier to test and rewire with them like that.
Don’t touch any bare wire or screw connections.

Don’t let switches touch each other or the metal box.

Keep kids and pets away.

Thank you, Jeff. I will try these steps. I've replaced many of the switches in my house but have not gotten to some of these yet. I do prefer to wire to the screw terminals when replacing. I have fully flipped both breakers that control the interior lights, front and back, in the shared switch boxes. Should I expect the exterior lights to be on these same circuits just because they share a switch box? I don't see any circuits in the main panel labelled "exterior lights". If the exterior lights did share a circuit with some other lights in the house, I haven't noticed any other lights not working. If this does not fix it, I will flip the power main. Do I need to shut down water heater/furnace and then turn back on after when flipping the main breaker?

 

[Jeff Handy]

Anything with a circuit board can sometimes be zapped by main power going on and off, so use your own judgement.

Do not assume same breakers control anything in the same box.

Outside lights are often controlled by a breaker marked Garage or Exterior Outlets.

Also, there could be a gfci outlet in the garage or outside that has tripped, check the reset buttons.

Or a gfci breaker in the panel that needs resetting.

 

[ekrig]

I second Jeef's point about an GFCI outlet. Often times, exterior lights and outlets hang off a GFCI outlet somewhere. The GFCI outlet might need to be reset or simply gone bad (they need to be replaced fairly often).

 

[MrMiz]

+1 for the GFCI's I have a set of exterior lights that are on a GFCI outlet in a basement bathroom. Nowhere even near the exterior of the house. It's a old house and the wiring has been redone in stages and that particular circuit was added after a fire. If the house has been remodeled look for a junction box. I've had some luck with finding loose connections in a box that was placed just to extend a circuit after a remodel. If they followed code it should be in a box with a blank cover plate exposed.
Also as a side note some motion sensor lights are "Programmed" by turning the switch on and off at set intervals. My mom has one that she constantly thinks has gone bad, but in reality she's just accidentally "reprogramed" it. Basically if you flip the power switch within 3 seconds. On, then off, then on it sets the light fixture into switched mode and works like a regular light. If you do it again at the same interval it changes it back to motion sensor mode. If I remember right their is a third option to set it to "dusk" mode, but I don't remember how to do that. I just set it back to motion mode for her ever time she calls about it. That's to say yours may have this kind of feature. I think Dusk mode is always on, but the light never turns on until it gets dark/dusk then stays on for a couple of hours and then reverts back to motion mode. I feel like I read that in the manual at some point.

 

[Jeff Handy]

One more gfci outlet tidbit of info.

When they first came out, if the sensor chip inside a gfci outlet failed, the outlet would still remain live, it just would not respond to a ground fault anymore.

Which was unsafe, people did not realize they were not protected against shocks.
And almost no one ever tests the outlets with the buttons.

So manufacturers had to change the sensor chip inside to permanently kill the power to the outlet, if the sensor chip went bad.

More annoying, but you won’t die from getting shocked!

Also, on newer gfci outlets, the Reset button is much stiffer, harder to push in to reset.
Just fyi.

 

[bbp]

Thanks everyone. There is a GFI in the garage. I flipped the breaker for it and also reset the GFI itself by pressing the test/reset buttons. The GFI outlet is still providing power directly from the plugs, so in that regard it appears to be working. I'm wondering if the GFI is in some strange broken state where the line side is functioning but the load has become defunct. I'm going to replace the GFI and see what happens.

 

[Jeff Handy]

If outlets are live, load outfeed should also be live.

Are there any breakers in the main panel with GFCI reset buttons?
There often are.
For whirlpool tub, bathroom outlets, and outside outlets or lights.
Check those buttons.

Are there any gfci outlets outside?
Check their buttons also.

Sometimes there is a forgotten three way switch in the garage, that also controls the outside lights.
And might be switched off or defective.

 

[bbp]

I've recently come back to this puzzle.

There are no GFCI breakers in main panel. There is a non-GFCI outlet in the back on the exterior of the house and it works fine. I have not seen any tricky hidden switches anywhere in the garage.

I've flipped every breaker in the box. I've flipped the main breaker as well. Today I replaced the GFCI outlet in the garage that was between the main panel and the front exterior lights hoping to get lucky. No dice.

I came back to one of the light switches that controlled the exterior house lights and tested voltage again. I got 2 volts across the switch in both positions. This seems odd as I would expect 0 or 120. What could cause 2V, a partial ground? I'm getting ready to call an electrician but I'm afraid they're just going to tell me we have to open the walls up.

 

[ekrig]

I had a similar situation when one of the GFCI inside the house went back, and the voltage at the downstream outlet would sometimes measure around 90VAC... In my case that GFCI was in a bathroom, and it worked ok there. Hence my surprise to discover that it provided current for multiple outlets around the house, including exterior ones.

I'd use one of those outlet checking devices with ability to trigger the GFCI and see what else looses current. My hunch is a GFCI will need to be reset someone and that will most likely be your culprit.