Attached is a markup picture to help identify wiring. This is in the USA. There are wires that come in from the bottom left of the box and from the top right of the box.

enter image description here

I'm just a DIYer, and I'm trying to replace a single-pole light switch that powers 2 outside lights (same switch on/off) with a smart switch to control these lights for "dusk to dawn".

I originally had the far left exposed cable and the far right exposed cable in the single-pole light switch.

  • I tested the far left exposed one (colored red line in the pic) and it registered 108-110v
  • I tested the far right one (I colored it blue in the pic but it's technically a black cable) and it read 0 (zero), so I'm assuming that is the load
  • I tested the middle white wire going into the 3 prong push connector and it read 0 (zero)

My Assumptions:

  • the source black power wire is coming in from the bottom left of the box and feeds into the connector on the left which supplies the local black wire power and also feeds additional power out the upper right to "somewhere"
  • the left most white cable in the connector comes from the electrical panel since it's with the source black wire that has power
  • the middle and right white cable in the connector are neutrals for each external light

Again, these are just assumptions...but seems reasonable.

My Question...how do I add a local neutral for my smart switch? Am I right in assuming the main neutral feed is from the left most white cable coming from the same part of the box as the black power cable that is hot? If so, do I just need to replace the 3 pin push connector with a 4 port connector and add a white neutral cable to it for the smart switch?

  • 1
    Profile location puts you in the US, as does the wire colors here. Helpful to mention since electrical standards vary widely around the world...
    – Ecnerwal
    Sep 25, 2022 at 21:23

1 Answer 1


I say your assumptions are correct. The neutrals can all be tied together with a pigtail to provide the neutral for your new smart switch.

  • Thank you for confirming my assumptions. It worked fine to replace the existing 3 pin push connector with a 4 pin and add a short white 12ga.
    – TheCleaner
    Sep 26, 2022 at 13:51

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