wiringI am trying to figure out which one of these 3 blue wires is the correct one to use as my C-wire.

I have a reg Honeywell thermostat but recently bought a WiFi Honeywell thermostat. When I pull original thermostat off wall I have red, white, yellow, and green connected.

There is a a blue wire there just wrapped in the back but not connected I'm assuming this is the C wire. But down in the Goodman furnace, there are 3 blue wires just wrapped around the bundles of wires and I have no idea what one is the correct one leading up to the thermostat.

Furnace end of wiring furnace end

2nd view of the furnace end furnace end 2nd pic

Old thermostat wiring. old thermostat

  • Can you post photos of the wiring at the furance end please? Jun 21, 2023 at 3:00
  • Hey so sorry for super long delay but here is photos of the furnace end. Please let me know. Thank you
    – Donald M
    Jun 27, 2023 at 23:33
  • 1) I only see 2 unused blue wires in your 1st pic. 2) Please post another pic showing what the wires from left cable in the first pic connect to.
    – FreeMan
    Jun 28, 2023 at 13:55
  • Can anyone help
    – Donald M
    Jun 28, 2023 at 21:32

2 Answers 2


I see a blue wire in the wall outlet that is not connected

That would be your C wire.

Use it and connect to the c label and Hope it is connected on the other side.

If not find it and connect

  • No the only thing connected in the furnace itself is a red wire to the C terminal on the circuit board. I don't know which blue wire down at the furnace connects to that terminal though
    – Donald M
    Jun 21, 2023 at 1:05
  • 1
    @DonaldM you are looking in the wrong spot on the circuit board. You have White, Yellow Green and Red already connected. Where is the Blue ? Also it should be in the Air handler not on the furnace.
    – Traveler
    Jun 21, 2023 at 2:15
  • @DonaldM Please do not edit answers in an attempt to respond to people. Please put your additional picture up in your question.
    – FreeMan
    Jun 27, 2023 at 23:52
  • Oops sorry I think I editied my original post and added the pictures now.
    – Donald M
    Jun 28, 2023 at 0:00

Follow the green

While your furnace wiring is quite the mess, since we know that there is only one cable there whose green wire is used, and that wire is connected to both G at the thermostat and G on the control board, the cable it's in must be the cable that connects the control board to the thermostat in your configuration. The other wires in that cable match up as well -- W goes off to the heating control device connected to the left-hand cable at the furnace, R lands on the R terminal, and the yellow Y wire is connected to what appears to be a condensate overflow switch. So, take the blue wire from that cable (which you already have pulled out somewhat), land it on C at both ends, and you're good to go!

  • Perfect thank you, I will try that tomorrow evening and let you know. Thank you for your help.
    – Donald M
    Jun 28, 2023 at 22:56

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