The brown wire connects to the Y2 terminal for the two-stage heating system, while the white wire goes into the W terminal for heating control. Understanding them is key to deciphering a wiring diagram. The white wire is for heating and is connected to the W terminal on the thermostat.
The switches and other controllers are placed on the left side of the diagram. Power supplies may be indicated by solid lines or by dashed or dotted lines. “Air Conditioner Wiring Diagrams”

