This is new work, and has not previously functioned.
I have three switches in a 3 gang box. 2 of these share a circuit, and have an odd interaction. The fan is connected to the box with a 3-wire which is independent of the 2 wire which connects the lights. The black wires from these two are connected to the terminal on Switch 1 with a pigtail.
Switch 1 is intended to power the lights in the area, including the lights on a fan.
Switch 2 is intended to power the fan motor only.
Switch 2 functions as expected.
When Switch 1 is flipped, the output terminal on Switch 2 is hot (tested with a voltage detector), regardless of the position of Switch 2.
Things I have tried:
I entirely disconnected the 3-wire running to the fan, and used a multi-meter to check for a pathway between any of the wires (I am unsure if this is adequate to assess is there is damage to the wire)
Swapped out Switch 2 in case it was in some way defective
I connected everything as I would expect to work, and used a multi-meter to check expected pathways with all configurations of Switches 1 and 2. I detected nothing
I am unsure what the next steps should be for debugging, and I haven't been able to google for this problem effectively. Thanks!
Details on the above image:
The third switch (right-most) is on a separate circuit (B). All grounds are shared between all three switches. The white neutrals with the yellow cap inside the box to the top left are for the circuit breaker relevant to that second circuit. The left two switches, those I am referring two as 1 and 2, are together on a different breaker (A). They share the neutrals that I pulled out of the box to the left.
Of the /3 going to the fan, the red wire is connected to the motor, which is going to the middle switch (2), and the black wire is connected to the light fixture (pigtailed with the other lights) on the left switch (1).