Long story short, I'm trying to install one sensor switch for both fan and light in the bathroom. I have one light switch outside the bathroom. Inside the bathroom there is 2 gang switch box with 2 switches connect. One is for the fan the other one I have no idea what it's for. It could be for the light but the light does not turn on or off with this switch. Is it still possible that it could be for the light but the switch is dead? The black wire is hot for the right switch. I took the plate off and tested it with non-contact tester.

Left switch is for Fan and Right switch is the one I can't figure out what it is. enter image description here Bathroom light switch from outside enter image description here

  • Can you trace where the cable going from the load side of the mystery switch goes? Oct 13 '17 at 1:32
  • One good guess might be to take apart the fan and find out if the other circuit also ends there. The original design may have been fan/light combo.
    – Tyson
    Oct 13 '17 at 3:20
  • Other than that you can disassemble and use a circuit toner/tracer to try and follow the wire behind the wall and see where it goes.
    – Tyson
    Oct 13 '17 at 3:34
  • if you turn the circuit off at the breaker, you can check for continuity between the terminals on the open switch; if there's none, it's likely not hooked into anything that will be missed. if there is, you might have heated floors
    – dandavis
    Oct 13 '17 at 6:11

I found out that the Fan and vanity light are not even on the same breaker. So this mystery switch is not for the light. I found out from previous owner that it may have been for a light before the bathroom was renovated.

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