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.
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.