I've seen other similar questions (How to trace mystery switches), but I have some more details:
- This is in a master bedroom
- There is a 2 gang box right near the inside of the door - one switch (purple wire and yellow wire) controls the overhead light. The other switch (purple wire and orange wire) is the mystery switch.
- There are no switched outlets (I tried with a lamp)
- There are no outdoor lights that I can notice (as suggested in the other answer)
- I bought a Fluke Pro3000, turned off the power (purple was power anyway), hooked the red alligator clip on the toner to the orange wire, and tried sweeping the wall with the probe, but it was inconclusive at best
- The pipe the orange wire enters from the box goes up
Any new guesses or suggestions of other experiments to do?