Videos of wiring a thermostat with 4 wires Click to view on YouTube9:47Upgrading from a 4 Wire Thermostat to a 5 Wire Thermostat199K viewsYouTube · 2 years agoClick to view on YouTube16:45Episode 65 Nest Thermostat E install 4 or 5 wire4 viewsYouTube · 8 months agoClick to view on YouTube1:32How to wire a thermostat with 4 or 5 wires31K viewsYouTube · 3 years agoClick to view on YouTube6:04Thermostat Wiring Diagrams! 10 Most Common!18K viewsYouTube · 5 months agoClick to view on YouTube5:174 Wire Installation Video Updated2 viewsYouTube · 2 years agoClick to view on YouTube0:52Honeywell Manual 4 Wire Premium Baseboard/Line Volt Thermostat (CT410B1017)21K viewsYouTube · 1 year agoSee more videos of wiring a thermostat with 4 wires 4 Wire Thermostat Wiring Color Code - onehoursmarthome The picture above depeicts the typical wiring color code for a 4 wire thermostat. The above is a typical wiring diagram of a Nest Thermostat with 4 wires. This is commonly found in standard HVAC systems that use an air conditioner and a furnace.Author: James Both 4 Wire or 5 Wire Thermostat Wiring Problem - Wifi Tstat 4 Wire or 5 Wire Thermostat Wiring Problem - Question: We have a 19-year-old condo with an old Carrier mercury thermostat. We have both a natural gas furnace and an AC unit. There are only four wires going into the existing thermostat - red, green, blue, white.