Car wiring diagrams: 1St Gen Nest Wiring Diagram, wiring diagram, wire wiring harness, schematic circuit diagram, wiring diagran, wireing diagram, wirring diagram, wiring daigram, wiring diagrams. Here s a step by step guide to help you. Take a picture of your current thermostat s wiring. Confirm that your system is compatible and get a wiring diagram. Install your Nest Thermostat. Switch off the power. Remove the cover of your existing thermostat. Check your system and get a wiring diagram..How to tell which Nest Thermostat you have st Gen, nd Gen or rd st generation Nest Thermostat. Installation Guide pages, .MB ..Your friendly, Heating, Ventilation, and Air Conditioning Repair Company! We re Precision Heating Air, LLC .