troubleshooting 3 way switches
Sometimes these can be a bit tricky. It's actually pretty straight forward. The switch doesn't have an on or off position like a single pole switch. It can be off in the up or down position. There are 3 terminals too! A regular switch only has two. We need three for a 3-way switch for the two circuits it has.
Follow the circuit through and you'll see it: go to 'start' at the black and white on the left top. This is power coming into the first switch. Lets say it's going to go through the switch on the green line, out on the red "traveler wire" to the other
3-way switch, through the green circuit and out to the light. Now if I switch the light on the left to the yellow position, the light goes off because the power moves to the black wire, but the other switch is still set for the red wire, so it's now off.
If I turn the right switch so it connects to the black, the light is back on. You can turn either switch to turn the light on or off because there are two circuit possibilities. You'll notice the white or "neutral wire" just goes through the boxes for the switches, it never gets switched, only the hot.
They use a 12/3 Romex cable that has a black, red, white and a ground for wiring between two 3-way switches.