One of the buttons is actually a 3-position switch that controls two different functions (light and night-light). This button controls the light on the fan so that it can be set to light off, night-light on, or light on. So your three switches have the following operations: Switch 1 - Heat On / Heat Off Switch 2 - Vent On / Vent Off Switch 3 - Light Off / Nigh-Light On / Light On.