I have a wall switch with two black wires. How do I replace

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with this new switch:

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  • 4
    What do you want to replace? If just the switch, then it doesn't matter which wire goes to which screw. Jan 16, 2017 at 18:49
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3 Answers 3


The current switch is set up as having a hot wire in (from the breaker box to the switch) and a hot wire out (from the switch to the light). The neutral / White wires should be pig tailed together in the box. There is also a green screw on the side, and this is for the ground.

Make sure to shut off the power before doing this (turn the breaker for the circuit off). Connect the top screw to the wire that feeds to the light. Connect the bottom screw to the hot wire. When you turn the power back on, and if you want to swap the direction of the switch (as in press down to turn off, or turn on), turn off the power and switch the two black wires.

  • 1
    It might be a three-way switch, but that can still work fine.
    – SDsolar
    Jan 16, 2017 at 22:20

I have the same set up and just installed a smart switch. Just follow the instructions that come with the new switch and have a voltage tester handy to determine which black wire is the "line" (hot) and which black wire is the "load" (switched hot).

Turn the circuit breaker off, pull the switch out of the box but leave it connected to the wires. Put it in the OFF position. Turn the circuit back on and carefully test which black wire has power running through it. The one that lights up your voltage tester is the line wire and the other is the load wire. Turn the circuit back off, label your wires and follow the new switch instructions.

  • Looks like the OP was trying to install a 3-way switch for a regular simple toggle. Your instructions for identifying the hot wire are spot on, but missing on the 3-way switch installation portion.
    – FreeMan
    Dec 21, 2021 at 18:56

Looks like the new switch might be a 3-way switch (or some type of smart switch). That's not going to work in this situation, since it looks like you're trying to replace a simple toggle switch.

  • 1
    It is a Decora switch, and the colors might well indicate that it is a three-way, but that can still work.
    – SDsolar
    Jan 16, 2017 at 22:19
  • 1
    All you have to do is use the black screw and one brass screw and a 3-way works just like a regular switch if you simply ignore the other brass screw.
    – Ecnerwal
    May 2, 2023 at 17:24

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