Wire A Thermostat - how-to-wire-it Wire a Thermostat, How to wire a thermostat, I will show you basic thermostat wiring, thermostat color codes and wiring diagrams. Wire A Thermostat. Be Sure To See My Low Priced Thermostat Store (Lowest On The Web) How to wire a thermostat. To wire a thermostat, you must first be aware of the type of system that you have in your home. Heat Pump Thermostat Wiring - Air Conditioning Systems Heat pump thermostat wiring - A typical wire color and terminal diagram. As shown in the diagram, you will need to power up the thermostat and the 24V AC power is connected to the R and C terminals. The color of wire R is usually RED and C is BLACK. C is known as the common terminal. These two connections will ensure that there is power to the thermostat that you are operating.