I am currently swapping out my switches with smart switches and one of the switches had different wire setup from the usual.

Prior to taking out the switch I took picture of the "primary switch" I quated/ say that cause when removing switches wire both had power in both areas.

Main switch enter image description here Look closely as the white wire and i believe the line wire are combined.

Secondary switch: enter image description here

I got the switch currently working and the on and off works on the light. But could some one tell me if you can make it out in the images what that red wire Is?

New Main switch: enter image description here

  • 3
    Light switches? Air-con switches? American? Australian? Not enough context.
    – Transistor
    Commented Aug 3, 2017 at 20:22
  • @Transistor sorry. They are Light Switches. American
    – RTarson
    Commented Aug 3, 2017 at 20:23
  • 2
    Look up 3-way switch on your favorite search engine's images. Commented Aug 3, 2017 at 20:25
  • @calcium3000 I did. It shows that red wire suppose to be a connection between light switches. But I have both red wires unplugged yet my voltage pen shows power
    – RTarson
    Commented Aug 3, 2017 at 20:27
  • 1
    Do you have a multimeter to test it instead? I wouldn't trust those voltage pens. Are you sure those red wires are the only ones in the circuit? They could be totally separate from the 2 switches you're messing with. Also, this could be a question for the Home Improvement SE. Commented Aug 3, 2017 at 20:38

2 Answers 2


That red wire is most likely part of a 3-way switch configuration, and not connected to the light at all. Disconnecting it would rid you of the benefit of this configuration -- i.e. both switches would have to be on for the light to turn on. With the red wire connected, either switch can turn on the light.

enter image description here

(A 3-way switch is an electrician's term for a single-pole, double-throw (SPDT) switch.)

  • 4
    A 3-way switch is an American electrician's term for a single-pole, double-throw (SPDT) switch. In Europe that's a two-way switch - up or down. In the USA they count the wires or terminals as "ways".
    – Transistor
    Commented Aug 3, 2017 at 21:22
  • 2
    3 ways to wire it and several ways to do it wrong including mistaking the Throw for the Pole. Commented Aug 3, 2017 at 21:34
  • Carter wiring e.g.
    – Janka
    Commented Aug 3, 2017 at 21:38
  • @Transistor since the OP specified American I tailored it to him. If it were up to me I'd call it a two-way as well. Commented Aug 3, 2017 at 21:43


simulate this circuit – Schematic created using CircuitLab

enter image description here

Note the switch closest to power source is lit all the time and remote switch is lit with bulb, due to internal light wiring on Pole or screw terminal furthest away.

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