enter image description here I am trying to replace a single pole switch with a fiet dimmer. However my box has 4 black and 4 white wires. I think the single black line-in is simple to identify and is connect to ac-l and ground to green. But the other 3 black wires are connected with wire nut. And 4 whites are connected as well. I added a neutral wire extension for ac-n. But still The dimmer is not coming on. What am I doing wrong? Thanks

  • Single switches/dimmers require two wires, one power in, and one power out(to light). Would guess you should have two blacks that connect to the switch, one might also be connected to other black wires( to power other outlets?).
    – crip659
    Commented Jan 28, 2023 at 18:33
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    Can you post photos of the inside of the box in question please? Commented Jan 28, 2023 at 18:47
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    How did you add a neutral wire extension? Do you mean what is called a "pigtail"? Which wires was the old switch connected to? Did it have a pigtail off the 3 blacks? Commented Jan 28, 2023 at 19:14
  • Photo posted, do I have the ac-l and load wrong?
    – Pshah
    Commented Jan 29, 2023 at 15:33
  • A better angle, with the wires more clearly separated, would help, along with telling us exactly what make and model the new switch is. I am guessing that you have swapped the unswitched hot and switched hot (doesn't matter for mechanical switches, does for smart switches), but that is strictly a guess; I'd disconnect everything, get out a meter, check which is really unswitched hot and check the switch's installation guide to make sure everything was connected at the right places.
    – keshlam
    Commented Jan 29, 2023 at 18:06

1 Answer 1


Sounds like a standard "pigtail". Power is coming into this box on one pair of black and white wire and being passed on to other circuits via the wire nut connections.

The wire nut for the blacks should have one short wire coming out of it; that goes to the dimmer's hot terminal. There should also be a black not connected to that wire nut; that goes to the dimmer's load terminal. So far, this is exactly the same way the switch was connected; if you took a photo before disconnecting the switch you can use that as a guide for connecting the dimmer.

If it's a smart dimmer it may need a neutral connection too. If you are replacing a smart switch, that may already be available as a short white wire coming from the wire nut trying together the white wires; if not you'll need to add that. You may or may not need a larger wire nut to allow for the added wire.

If this was a smart switch and the dimmer you're putting in doesn't need neutral, that short white wire will be present but isn't needed. Rather than undo and redo the wire nut connections, you could just cap this wire with a wire nut to keep it from shorting to anything else; that may be easier.

Diagrams illustrating this can be found in some of the other Answers that discuss replacing switches. Essentially the dimmer is just a fancy switch, for wiring purposes.

  • You are absolutely right keshlam I added a white wire for the neutral the hot and load wires from the old switch were reused as is. But it still didn’t work. Anything to do with the ground? The ground also moved as is. I have pictures I took but not sure how to add here.
    – Pshah
    Commented Jan 29, 2023 at 1:31
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    If you Edit your post, you should see a group of editor icons at the top of the text box. One of them is a stylized landscape. Clicking in that should let you insert/upload images. You may need to resize large images before they can be uploaded; you'd need to do that on your own machine first, if so.
    – keshlam
    Commented Jan 29, 2023 at 16:28
  • Image posted. Thanks
    – Pshah
    Commented Jan 29, 2023 at 16:50
  • The wire labeled "AC-L" was probably supposed to be the load, assuming whoever installed the previous switch labelled it correctly. The fact that itt a thinner wire alsi suggests that it's left over from the previous switch...
    – keshlam
    Commented Jan 29, 2023 at 18:08

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