I have looked at other responses and each layout is a little different. Looking to connect a Smart Thermostat and need to know where to connect the Blue wire at the Furnace. See the attached picture. Lots of possibilities. Thanks for the help and guidance.

enter image description here

  • 1
    Possible duplicate of How do I identify the C terminal on my HVAC?
    – Machavity
    Feb 19, 2019 at 18:36
  • Thanks for the link to the article. My unit doesn't have labeled terminals, just wires twisted together with wire nuts. Sorry, but I did not really understand the schematic or transformer section. Perhaps it's not that simple, but was hoping to know which of the 6 wire nut combinations I should add the Blue wire to in the picture. Red/Yellow, Red/Black, Green/Green, Blue/White, Brow/Tan/White, Red/Black/White. Thanks again.
    – MSykes
    Feb 19, 2019 at 19:03

1 Answer 1


The wire nut on the far right is your common. Test it before you power up your stat. You can test it by attaching test leads from the red to the blue coming from the furnace. You should get 24v.

  • Thanks Joe, The far right is the Blue/White combination. Much appreciated.
    – MSykes
    Feb 19, 2019 at 19:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.