I did 2 things. First I combined 2 existing light switches into 1 via a metal box twisting the black wires together into 1 group and then in another group twisting the white wires together. That worked fine.

Then I added a new light that I installed to the same groups of wires in the metal box, matching the colors up. However, when the switch is on, the existing lights are on but the new light is off. When the switch is off, the existing lights turn off but the new light turns on.

I've tried several things including a different light switch and reconfiguring the wires a few ways, but same result every time.

I've added a picture showing the current configuration. The thick black wire in the top left is the source. The hot wire is directly from the power source. The neutral leads to 3 lights. The thick white wire on the right leads to the new light fixture but is not currently connected.

Why is this happening? What should I check?enter image description hereenter image description here

  • 2
    Can you return it to its original condition and take a few pictures and post them?
    – JACK
    Commented Jun 12, 2020 at 18:35
  • 1
    Yes, can you post photos of the insides of the boxes involved please? Commented Jun 12, 2020 at 19:31
  • 1
    Are you using a 3 way switch with the hot on the wiper or common contact?
    – Ed Beal
    Commented Jun 12, 2020 at 19:40
  • 1
    "combined 2 existing light switches into 1" What does that mean, how did you do that?
    – Alaska Man
    Commented Jun 12, 2020 at 19:54
  • I will post pictures if still not working once I continue on this.
    – bluejaywpg
    Commented Jun 13, 2020 at 3:05

2 Answers 2


What you did was to place the new light in parallel with the switch, instead of in parallel with the existing lights. With the switch on, the new light is shorted out and and the old lights get power. With the switch off, you have the new light in series with the old lights. I’ll bet the the new light is very low wattage (e.g. LED) while the old lights are high wattage (incandescent). The low wattage light gets almost all of the voltage and the high wattage light gets so little that it doesn’t visibly glow.

As @isherwood noted, what you have in the box is a switch loop (actually two, but that’s beside the point). What you need to connect to is the switched hot and neutral and the only place you’ll probably find those is at one of the existing lights.

Edit to add more details:

Here's the wiring called a switch loop:

enter image description here

The power enters via the black (hot) wire into the fixture box. It continues into the switch box via the white (with black tape) wire to the switch. When the switch is turned on, the power continues back up the switched hot (black wire) to the light. After the light, the power returns to the source on the white wire (neutral).

Depending on the age of the installation, there may or may not be an additional white wire carrying the neutral into the switch box. This is to allow the use of smart switches which require a neutral but in your case, would not be connected in the switch box, but just capped off.

The power could also enter via the switch box, in which case, it would look something like this:

enter image description here

The difference here is that the hot directly enters the switch box and goes to the switch. The switched hot continues up to the light. After the light, the power returns on the neutral to the switch box where it's spliced to the neutral back to the source.

You need to connect the new light between the switched hot and the neutral. This is the only way it will work correctly. Here's how to tell where that is.

If there were no extra white wires in the switch box or there were just one or two (one from each existing light) not connected, then you have a switch loop: you cannot connect the new light at the switch. Instead, you must connect to one of the existing lights, back to the black on the light and white to the white on the light.

On the other hand, if there where two sets of white wires, each connecting through (spliced with a wirenut or such), then the power is first arriving at the switch and you can connect there. Connect your new black to the side of the switch going to the lights (if you can't tell, try one. If the switch won't control the light, switch it to the other). Your new white connects to the spliced whites in the switch box: remove the wire nut, add the new wire and re-attach it. You may need a larger wire nut but just going from 2 to 3 wires, probably not.

Note: I have ignored details such as how to connect a wirenut and have ignored the grounds. You must properly connect the grounds assuming there are ones there (maybe not on very old installations).

Hopefully, this is enough to help you. If you are still lost, I'm afraid you need to call a professional: an electrician or, for this, maybe a handyman. Please don't experiment. House wiring voltages or currents make it just to easy to kill yourself or someone else or to cause a fire! Be safe!

  • Actually, all 4 of the lights are CFL. I'm not sure I understand some of what you said due to my unfamiliarity with the terminology (parallel, switched hit and neutral) or why I have a switch loop.
    – bluejaywpg
    Commented Jun 13, 2020 at 3:03
  • @Jay Please see my edits.
    – DoxyLover
    Commented Jun 13, 2020 at 4:22
  • OK so I'm revisiting this finally and I'm trying to understand what you posted on your edited comment because I want to learn. I've been matching the wire colours but I noticed in the 1st picture that there's a black connected to a white. I'm curious why, but I'm not concerned about it right now because I believe the power enters the switch first so the 2nd picture is what applies in my case. I will try to duplicate the 2nd picture and I'll let you know if I have any questions. Thanks.
    – bluejaywpg
    Commented Jun 23, 2020 at 23:31
  • So I finally rewired this according to the picture you attached. The result? Only the new light turns on. If I remove the new light & attach only the old lights to the switch, the old lights all work fine. Why?
    – bluejaywpg
    Commented Jul 18, 2020 at 1:03
  • I tried 2 different ways to follow the diagram by essentially adding the new light as a continuous path in the circuit. It goes from hot line in to the switch to the new light to the old lights via the neutral line. No matter what, only the new light works. When I remove the new light, the old lights work again.
    – bluejaywpg
    Commented Jul 19, 2020 at 18:45

I think you've merged two switch loops (and possibly two distinct circuits) with your original action. That was probably incorrect and should've been done with a double-pole switch. You're lucky you didn't combine circuits from two phases and made big sparks.

I also suspect that you can't simply add a new switch there because you'd then have two devices wired in series.

  • 1
    Well, you just need a double pole switch, not double throw, unless there's three-way switching involved... Commented Jun 12, 2020 at 19:45
  • There is no 3 way switching involved. The 3 original lights that were on the 2 original switches that I combined into 1 switch appear to be on 1 long circuit based on my earlier tracing, and everything is confined to the same circuit breaker. I'll try a double pole switch from the store and see what happens.
    – bluejaywpg
    Commented Jun 12, 2020 at 20:53
  • The double pole switch is not working as the existing lights still work but now the new light doesn't work at all. What do I have to do? Do I really need a double pole switch?
    – bluejaywpg
    Commented Jun 23, 2020 at 23:34

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