I’m trying to figure out what is going on here, it seems as if either the load or line feed is going into the 4way box in the middle rather than one of the 3way boxes at the ends. There also appears to be a white (neutral?) wire that is capped to itself doing nothing in that same 4way box. At first I was thinking this was a red herring as there is an outlet below the “side door” 4way switch, thinking maybe they were just tapping off the switch to power that outlet or something but I’d need at least 6 runs for a 4-way so it must be either the line in or the load?
The house was built in '85. None of the single switches in the house have neutrals, only the multi-gang boxes do. The “upstairs” light is currently an illuminated dumb switch. I know that will need to be replaced for a regular dumb switch but didn’t know if that would help with this puzzle at all for reasons I don’t understand yet.
Pretty confident I’ve figured out the problem. The wire coming out of the bottom of the “side door” switch box was an attempt by someone to feed an outlet from that switch. The outlet did not work (how could it with only one wire attached…) The white wire on the outlet has conductivity to the capped white in the switch box and I’ve removed the black wire from that bundle and capped it as well and there is no change for the lighting at all. I think what I have here is a regular old non-neutral setup with a confusing red herring outlet with my line/load loop being at the “back door” switch box. Time to order some aux switches (bummer, I bought the Inovelli dimmer specifically to allow me to use the dumb switches) but such is life. Hopefully I don’t run into the ‘dimmer min/max needing to be set or the aux switches won’t work’ issue that I’ve been reading about with non-neutral setups.
Glad you got it figured out. A 4-way leg with power to the 4-way switch box is/was not all that uncommon. You start with a hot and neutral fed to the box with the 4-way switch and then send the switched hot out through all the 3-way switches, where it makes its way switched up to the light, which also has to be fed from the 4-way switch box via a 2-wire.
Looks like this:
If you have this then it’s a simple neutral config w/Aux switches.
A variant of this is where you feed the light first and then send it to the 4-way box. That sucks, because then you have a non-neutral in the 4-way box.