How to Connect Thermostat Wiring. Putting in a digital thermostat helps control your heating and cooling bill and maintains a more even temperature throughout your home. You can buy thermostats at a local hardware store and, in about an hour, you can improve your home's energy use.
Turn off power to your thermostat. Not all thermostats have a power supply. For example, non-digital or battery-operated thermostats don't have power supplies. You can flip the breaker for the room if you are unsure.
Remove the face plate of the old thermostat and unscrew it from the wall.
Mark all wires before you remove them from the unit. You can do this by writing the corresponding letter on masking tape and taping the wire to the wall. Color-coded wiring doesn't always work with new thermostats, so label them carefully.
Match your labeled wires to the new unit and attach them in the right places.
Mount the back plate to wall. If the new thermostat is a different size from the old one, you must drill new holes. Make sure that the new holes are level to prevent any errors in the thermostat operation.
Install new batteries if needed and program the thermostat.
Check the thermostat with a level. It must be level to work correctly.