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In brief: in replacing an old light switch in an old house with a GFCI combo switch/outlet, facing existing wiring that doesn't quite match instructions, I get the GFCI outlet working but not the new light switch. What else do I need to test or install?

Gory details

I'd like to replace an existing light switch with a Leviton combination GFCI outlet and switch.

On one side of the old switch, I find

  • black wire #1, confirmed hot with my voltage tester, pigtailed with

  • black wire #2, confirmed not hot, going I know not where

On the other side of the old switch, I find

  • black wire #3 (that I see runs into a white sheath in the box), also confirmed not hot.

The old switch works, and when I patch black wire #1 and black wire #3 together (circumventing the switch) the light goes on, so I know that black wire #3 is the load wire for the light.

I also see that the box contains three white wires that have been capped together.

After some back-and-forth, I've correctly wired the GFCI outlet:

  • black wire #1 into the GFCI Line hot terminal

  • pigtail capped into the three white wires into the GFCI Line white terminal

My GFCI tester says that works, and it tests/resets fine.

However, no matter how I wire the switch leads or set the switch, the light stays off.

I'm following the "two cable" instructions, since I have no downstream outlets to connect.

The receptacle has two black leads for the switch. Per instructions,

Connect the switch leads to the switch controlled LOAD (not GFCI protected, shown in diagram):

  1. One black switch lead connects to the LINE side black wire.

  2. The other black lead connects to the HOT side of the LOAD.

  3. The LOAD must be properly connected to NEUTRAL and grounded.

This puzzles me in two ways: first, that it doesn't seem to matter which lead goes to the load wire of the light and which to the line wire, and second, that, in my situation, I can't be certain that any of the white wires in the box are the Line (return) from the light.

I've tried wiring the receptacle switch leads in various ways, none of which got the light on, ending with this configuration which seemed most correct:

  • first black lead capped with a pigtail connected with the original 3 white wires (instruction #1)

  • second black lead from the receptacle capped with black wire #3 and a wire grounded on the box (instructions #2 and #3)

I'm also not certain what to do with black wire #2 above. I've capped it with black wire #1 and connected both with the GFCI Line hot terminal. The GFCI outlet continues to work fine, but no joy on the switch.

What else do I need to test re the existing wiring?

How do I get the switch to work?

  • Can you post some photos of the existing wiring situation? – ThreePhaseEel Dec 14 '16 at 23:15
  • Also, with the circuit OFF at the panel, can you measure the resistance from Black Wire 3 to the bundle of white wires? – ThreePhaseEel Dec 14 '16 at 23:17
  • Do you need the lights to be gfci protected? – Tester101 Dec 15 '16 at 2:32
  • The images on this answer might be helpful. – Tester101 Dec 15 '16 at 2:34
  • The switch in this device is not connected internally to anything except the two permanently attached wires. Most of the published wiring methods for this device will not work if the switch has any internal connections. – A. I. Breveleri Dec 15 '16 at 3:09
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Two devices in one package can make for twice the confusion

GFCI/switch combinations are a common cause of DIY confusion, as they have more, and more varied, connections than most other electrical devices one can get at the hardware store.

In your case, you have the GFCI portion wired correctly, but the switch is what has you down. It's actually nothing special, just a plain single pole switch with no internal connections whatsoever to the GFCI. However, you seem to have your hots, neutrals, and grounds confused with regards to the switched load. What they mean by "The LOAD must be properly connected to NEUTRAL and grounded." has nothing to do with the wiring in the GFCI box -- in fact, the wiring of the switch to neutral and ground is why the switched load isn't working right now! It simply means that the load itself must be wired correctly and not in a bizarro way (such as across two hots, from hot to ground(eek!), or with a switched neutral). In fact, right now, the load can't work because there's no voltage across it with one end wired to the neutral (and ground) and the other wired back to that same neutral.

To get this all working I would:

  • Disconnect the switch-wire going to the white wire bundle from the white wire bundle, and remove the pigtail from the switch/black wire #3 junction to ground.
  • Cap off black wire #2 by itself since you don't yet know where it leads. (Sooner or later, you'll find the thing that doesn't work, and then you'll know what that black wire was feeding.)
  • Connect one black wire from the switch in with black wire #1 and a black pigtail to the GFCI's LINE HOT terminal.
  • And connect the other black wire from the switch to black wire #3.
  • I did exactly this and it works perfectly. For extra credits and all the upvotes this newbie can give (if any): it doesn't seem to me that the switch could work as indicated in the instructions. There's no hot wire running into the switch, if you follow the instructions. – Citizentools Dec 15 '16 at 17:34
  • 1
    @Citizentools -- the LINE side black wire is the hot wire for the switch. – ThreePhaseEel Dec 16 '16 at 0:12

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