I currently have a 3 way light switch in my stairwell. One at the bottom and one at the top of the stairs. I recently added a light fixture to the bottom of the stairs but need some help wiring it up. I have been rewiring the whole house but the 3 ways a bit confusing to me. Power comes in from the light fixture at the top of the stairs. Here is a diagram of what I have and what I am trying to do. Any help would be great. enter image description here

enter image description here Can I tie into the wiring leaving the original light before it reaches the switch on the left?

  • 1
    You can't do that. 3-ways do not work that way. – Harper Mar 15 at 13:24
  • Nope, sorry, can't do that one either. You need netural and switched-hot, and neutral is not at either 3-way location. – Harper Mar 15 at 15:30
  • So it has to be from the power source feeding the original light. – Otten33 Mar 15 at 15:32
  • Yes, unless you are able to change the cable in the wall. You cannot just run a loose wire, the cable needs to be changed. If you could change the cable from the lamp to switch1 to a /3 cable, that would allow you to feed it from switch1. – Harper Mar 15 at 15:34
  • That might be easier for me to do. I'm working with plaster and lathe walls and have been just knocking holes in the wall and will patch them later. However, I would have to punch a lot of holes to get the cable from the bottom light to the top light as they are on different ceilings. I can however get to the top light switch without too much difficulty. – Otten33 Mar 15 at 15:46

Smart switch; change one cable

The cable from the existing lamp to the nearer switch (upstairs?)... you need to change that to a /3 cable (red white black).

You can extend the cable to your new lamp from any switch box. When you do, use colored tape to re-tag the black wire as a red wire.

Now we're going to fit smart switches that allow wireless connection of remotes. These smart switches cannot require a wire for comms between them, as we lack any spare wires.

Now we're going to change the color codes. As it happens, the existing color codes will suffice in all locations:

  • black = always-hot
  • white = neutral
  • red = switched-hot

Your master smartswitch attaches to black, white and red.

Your remote smartswitch attaches to black and white only.

Your original lamp connects to red and white.

Your new lamp attaches to red and white in the box nearest it.


Please clarify: is there an existing light fixture which is working properly with the existing switches? If there is, you need to run 2-wire from it to the new fixture and from the new fixture to the existing box on the left in your diagram. Wire both light fixtures in parallel, i.e. the white return to mains power goes to both, and the black output of the left-hand switch goes to the hot side of both.
This does mean you can't "cheat" as in the diagram which uses a single 2-wire cable for both the mains Hot input and the returning Hot to the light fixtures.


To be crystal-clear, another diagram from the same source as the one you posted. 2lights, 2 switches

  • Yes there is an existing light fixture and 3 way switches that work properly until I try and wire up the new light fixture. I've tried all kinds of wiring configurations and I can get the lights to work but not properly. New light will light up and the original light up top will light only dimmly from bottom switch. From top switch the top light will light up but not the bottom light. – Otten33 Mar 15 at 14:02
  • So I need to run 14/2 from new light to the old light? Is that the only way? This is in a staircase where one light is at the top of the stairwell and the other is at the bottom of it. I can probably reach the left hand switch without to much difficult but the top light might be a PITA. – Otten33 Mar 15 at 14:04
  • Yeah, I'm afraid so. – Carl Witthoft Mar 15 at 14:05
  • Can I tie into the wiring from the original light before it reaches the light switch on the left? Meaning right above the left hand light switch or does it have to be from the original power source running to the top light? – Otten33 Mar 15 at 14:12
  • @Otten33 Your main issue is that there is no neutral in the switch box you have the orange arrow going to. That's why you cant wire directly to that box. The box that has the first light in it is the only box with a neutral in your diagram. – JPhi1618 Mar 15 at 14:50

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