I'm replacing a regular light switch with a new dimmer switch. When I pulled out the switch, there was a red and black wire that were slotted into the top of the switch, and then a thicker black wire slotted into the bottom. And the grounding wire. The new dimmer switch has a green and white wire - I know the green wire is the grounding wire but don't know which of the black and red wire from the outlet is the neutral and which is hot. Also, on the side of the dimmer switch are spots for Load and Line. So I have 3 wires to connect to the white (neutral) wire, the Load and the Line on the dimmer...

  • 5
    Black and red aren't going to be neutral. There are no neutrals with a conventional switch. One likely comes in from the source and one goes out to another branch of the circuit. Please post photos so we can be sure what we're telling you.
    – isherwood
    Aug 20, 2020 at 20:21
  • 1
    Are you installing a smart switch/dimmer? They would have a neutral, white wire.
    – JACK
    Aug 20, 2020 at 20:22
  • Will the dimmer a light fixture or an outlet?
    – JACK
    Aug 20, 2020 at 20:26
  • 1
    Could you define what you mean by slotted , I ask because if backstabbed a larger wire size should not fit backstabs.
    – Ed Beal
    Aug 20, 2020 at 22:39
  • 1
    Can you post photos of the inside of the box please? Aug 20, 2020 at 23:57

1 Answer 1


You need to use a voltage tester while the circuit is on to identify which is the load and which is the line. The line comes from the circuit break to the switch. As long as you have power, that will be hot. The load is from the switch to the light/outlet/etc. That will only be hot when the switch is in the on state.

Neutral is its own wire. Generally white, and will be in the back of the junction box capped (unused). You connect the smart/dimmer white wire to this wire.

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