u/brickonwheels

Forgive my diagram, but ever since I moved into this house, a hallway light only turns on if the downstairs switch is down and the upstairs is up. Any other combination results in the light being off.

I used a voltage tester on each switch in the various positions and found that in two scenarios, the discards switch has power at all three wires with the light being off.

Can anyone help me trouble shoot what’s going on? The house is 120+ years old so the wiring is far from being color coded.