Split level house was built in the 70s and has a 4 way switch and a single pole right by the front door. The siblings to the 4 way are top and bottom of the stairs. The single pole controls the porch light.
I've identified the source line and the leg running to the porch. However there is something wrong with the 4 way.
As you can see in the picture, this is a 3 way switch, which led me to believe that it is either the first or last switch in the line up. When I looked at the other switches, the top of the stairs is a 3 way switch. The junction box only has a single 14/3 with red to bottom right, white to top and black to bottom left. Too dark to confirm without disconnecting everything, but it looks like the same style as the middle switch with the travelers on the bottom and common on top. The bottom of the stairs has a 4 way switch, but it shares a junction box with another circuit that I couldn't shut off so I didn't take it all the way out.
Back to the one that I'm working with, I've tested it with the circuit on and the only live wire is either the bottom red or black, depending on the state of the other 2 switches. That matches what I know about 4-ways. However, it has two lines going into the common. That, and the dead end on the switch upstairs, I don't understand.
Is this up to code? If it is I don't need to change anything expect add a spur from the line feeding the porch light to a transformer.
I think I figured it out. Fixed my typo with 18/3 vs 14/3. Mixed up because I ran the 18g for the doorbell. Also had to resize picture to be under 2mb. Attached now before I took anything apart. All markings on all wires are from me trying to figure it out.
Bottom of the stairs has a 4 way switch with line voltage coming in. Middle of the stairs has a 3 way, with separate line voltage coming in for the light outside, with a single pole. Top of the stairs has a 3 way switch.
Does that make sense? I can't figure out why the top switch can turn off the light if turned on from the middle or bottom switch. It must run from the middle switch, up to the light then back down to the top switch. Yikes. I've previously replaced the fixture above the ceiling and I don't remember seeing anything up there that set off alarm bells but now I want another look.
Whatever, it works. I just very carefully marked each wire with what terminal it is connected to and didn't mess with it. Replaced the double gang with a triple, but forgot to get the divider plate for the low voltage side, so I haven't put the transformer in yet.
Edit 2. The brown wire is 18g that is going to the doorbell. In the picture I already took out the plastic 2 gang already, but you can still see the metal bracket in the back it was mounted on. Hate those things, take forever to get out. I've replaced it with a 3 gang box but haven't been able to find anywhere local with divider plates so the transformer isn't hooked up yet. I want to put the transformer inside the box so it doesn't make contact with the foil from the insulation.