Honeywell Thermostat 4 Wire Wiring Diagram | Tom's Tek Stop WarningMulti Stage Heating and Cooling SystemsHoneywell Thermostat Wiring Diagram 4 Wire ExamplesRelated PostsSuggested ReadingReferencesRevision HistorySometimes even for the above common color uses, the exact purpose of a wire is often not clear. Not every four wire t-stat setup follows these “standards.”So again, if putting in a new t-tat, DO NOT rely on the wire colors alone! Repeating: DO NOT RELY ON THE WALL WIRE COLORS ALONE TO FIND EXACT WIRE FUNCTION. Instead, take a picture or write down which lug on the old t-stat that each wire goes with. For each wireSee more on tomstek 4 Wire or 5 Wire Thermostat Wiring Problem Step-by-Step Fix 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. 4 Wire thermostat Wiring Diagram | Free Wiring Diagram Variety of 4 wire thermostat wiring diagram. A wiring diagram is a streamlined conventional pictorial representation of an electrical circuit. It reveals the parts of the circuit as streamlined shapes, and the power and also signal connections in between the gadgets. Wire A Thermostat Y - Yellow Wire (For Cooling Enable) G - Green Wire (Controls Fan ON-Auto) The diagram shows how the wiring works. However your connections may seem a little different on the thermostat itself. Just take a look at the picture below the diagram. The RED wire or 24 Vac power lead is connected straight to the RC & 4 terminals. How to Wire a Furnace Thermostat With 2 Wires | Hunker Most two-wire thermostats wire have a red and white wire encased in a brown insulated coating. Strip the red and white wires back about 1/4 inch at both the thermostat and the furnace ends. Connect the white wire to the "W" terminal on the furnace and thermostat.