I have two existing dining room lights that are controlled via a three switch.
The existing wiring has two switch locations:
- Box 1 (garage)
- One 12-2 romex (black to black terminal on 3-way)
- One 12-3 romex (black and red on travelers, white wire nutted to white on 12-2)
- Box 2 (Hallway)
- One 12-3 romex (black and red on travelers, white on black -- not marked as hot)
I assumed then that the feeder was coming into box 1. I ran a new 12-2, pull the old box, put in a 2 gang box, and added my new single pole switch.
I removed the black wire (Original 12-2) and made pigtails, landing one back on the 3-way black terminal (where I pulled it), and landing one onto the bottom terminal of my new single pole switch.
I add the white from my new 12-2 into the wire nut of the old 12-2 + 12-3 to carry the neutral to the new light. The black from the new 12-2 I land on top of the single pole switch.
To wire in the new light, I removed the old light and removed the pigtails it had to the neutral in the box, and old hot from the 3-way switch. I pulled my new 12-2 from box-1 into this ceiling box and wired the new light directly to its black and white.
When I test the 3-way, the single light remaining on it works as intended. The new single pole switch however, does nothing. Then I notice, if I flip the 3-way to the "off" position (no power through the 3-way to the light) the single pole switch works.
I pulled my switches from box-1 and and checked the existing 12-2 with my meter, it has 120vac on it at all times (regardless of what position I put either 3 way in). I land that "hot" wire directly on my single pole switch and it works as intended. The moment I take a jumper from and touch it to the 3-way, the single pole switch stops working.
I'm at a loss for other things to try for troubleshooting. Any ideas / thoughts would be helpful.