Why does my 3-way, switch looped light not work properly?

Question

I'm trying to understand why a switch loop in my house was wired in this manner and if I need to correct it. I'm assuming it is incorrect because I cannot turn the light off and on from both switches. I included a diagram of the current wiring I can see and pictures of the switch receptacles. I'd like to avoid running new Romex if possible. The source comes into the light socket via the attic (Black and White only,) down to the first switch, and down to the second switch. Black, White, and Red wires are present with no ground between the switches.

My plan was to swap the bulb out with a recessed light fixture. I'd love to be able to add a smart switch in eventually, but it's not a dealbreaker. I need to hook up the light as well so guidance on that would be appreciated! Thanks!

First (Left Switch)

Second (Right Switch)

This is within the first switch box.

To First Switch (Left in Diagram)

Source

Answer 1

Let's review how 3-ways work.

Note the 2 travelers: one is hot, and one is not. They must necessarily always be in the same cable, and be the same on both ends.

That uses up all the brass screws and leaving only 1 screw left per switch.

Once you get the travelers right, there are precious few wires left. Hooking up the remaining wires is fairly obvious.

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Now, there's one wrinkle. Because it's a switch loop, neutral is not present in either cable. And when neutral is not present, there are strict rules about what white can be used for.

• It must be used as the always-hot if always-hot is present in the cable.
• Otherwise it can be used as a traveler. It can never be used for switched-hot.

So the black-white splice is actually a Code violation.

I recommend you rearrange the wiring so that white is always-hot "all the way". That means black and red are your travelers. So, #1 Rearrange the switch wiring so that black and red (from the same cable) are the travelers on the brass screws.

Then #2 break up that black-white splice that should have never been, and splice white-white.

Then pretty much a victory lap... both common terminals are empty at this point, so #3 hook up the remaining 1 wire in each box to the common terminals.

Up at the lamp, make sure you splice supply-hot to the white wire in this cable (so the black-white splice occurs there)... and use the black from the 3-ways as the switched-hot.

Answer 2

Try testing each switch to make sure you have assigned the correct wires to the correct screws. Disconnect all wires (mark them so you know which was connected where!) and then use a voltmeter in "ohms" mode as follows. Connect the probes to any 2 screws. If flipping the switch causes the resistance to go from zero to Infinite, then you have one probe on the single side and the other probe on one of the "double" side screws. Move one of the probes and test again. If flipping the switch does not ever give you continuity, i.e. zero ohms, then those two are the "double" screws and the third is the "single" side.
Once you know that, assuming the switches function properly, you can reconnect the wires to the proper screws on each switch. If the light still responds to only one switch, then the wiring for that light does not go to the other switch.