Here is a tight, safety-first wiring guide built around official dimmer instructions and a clean step sequence:
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The extra one is on a differently colored screw, and that screw decides whether the light dims from one doorway or both.
What follows covers how to install a dimmer switch in that order, starting at the breaker.
Do You Need To Shut Off The Breaker First?
Yes — power goes off at the breaker before the wallplate comes off, and a voltage tester confirms the box is dead before you touch a wire.
Start at the panel and flip the breaker labeled for the room; if nothing is labeled, cut the main. At the wall, remove the wallplate — two screws, or a flathead pried under the bottom edge on a screwless plate — then unscrew the old switch by its mounting ears, not by the wires.
A chirp means you flipped the wrong breaker, or a second circuit runs through the same box.
Wiring A Dimmer Switch: Which Lead Goes Where
Ground is the one connection with no judgment call.
A single-pole circuit — one switch, one light — is the easy case. Three-way circuits are where installs go sideways. That odd-screw wire is the common, and the dimmer’s common lead has to land there.
Small details decide the rest.
Model beats brand. Lutron’s Wiring Wizard builds the correct diagram for your exact model and switch count.
If the old switch is coming out anyway, our tested dimmer switch roundup covers which models fit single-pole, 3-way, and smart setups.
| Wire Or Terminal | What Connects There | Why It Matters |
|---|---|---|
| Bare copper or green ground | The dimmer’s green lead | Required by every major dimmer instruction sheet |
| Wire on the odd-colored screw (3-way) | The dimmer’s common lead | The light will not respond from both locations if this is wrong |
| Pair on the matching screws (3-way) | Traveler leads, either order | |
| Line, hot from the breaker | The dimmer’s line lead | Dead only after the breaker is switched off |
| Load, running to the light | The dimmer’s load lead | Single-pole circuits only
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