How do I wire a dimmer switch to replace my existing old switch? Dimmer has with 1 green wire and 2 black wires . My existing light switch has 1 black and 1 white.

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    Whoever wired the switch originally was lazy and neglected to put black paint or tape on that white wire; the reason to do this is precisely to ensure that future homeowners don't have to ask your question! You might fix that person's mistake and color the wire appropriately. – Eric Lippert Dec 5 '15 at 23:33

The white wire to the switch should be the hot feed if it is wired according to code. Connect the white wire to the top black wire on your dimmer and connect the black wire from the cable to the other black wire. Connect the green to the bare wire on the cable (and to the box if it is metal.)

Make sure your light fixtures are dimmable and the dimmer is the right one for the type of lighting you have.

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  • +1 You gave the right answer (mostly - SPs answer points out that most dimmers don't care which wire is which) . The white wire should also be marked with black tape or marker. – bib Dec 5 '15 at 19:39
  • The dimmer doesn't care but we do. We always top feed the switch like with a disconnect. – ArchonOSX Dec 6 '15 at 1:38

What you have at your switch box is called a switch loop. The feed should be brought to the switch on the white and the black is the switched wire.

With your basic dimmer connect the white to one wire and the black to the other. It does not matter which.

Green/bare is ground and should be connected.

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