I'm trying to install a new wifi thermostat, but am a little confused. I have 5 wires, but none are connected to the C in the thermostat, as seen below: thermostat

Additionally, when I trace the thermostat to inside of the Williamson furnace, it appears that the yellow/white wires are the ones connected to transformers, as seen below: furnace

And here is the thermostat wire hooking into the "panel": thermostatconn

Is there a configuration of the existing wiring I can use to power the new thermostat? (I've also purchased a 24v transformer, but am unsure of how to complete the circuit if I add one of the wires to the C terminal.)

Wiring diagrams below: wiring diagrams

  • 1
    Can you post the wiring diagram for your furnace please? It should be on a label on the inside of the access cover or such... Feb 23, 2021 at 1:48
  • Just added them - thanks @ThreePhaseEel
    – sorrell
    Feb 23, 2021 at 2:25
  • Can you get us more photos of the wiring at the furnace please? The last installer left us with a bowl o' spaghetti to sort out Feb 23, 2021 at 2:31
  • 1
    if that's the thermostat cable in the middle of the second photo I can't see how it ever worked,
    – Jasen
    Feb 23, 2021 at 11:37
  • @ThreePhaseEel - Noting that Jasen (thanks Jasen!) said it couldn't work, I located where the thermostat wire connects. It's in the picture above, but not easy to get a good pic of b/c the fan blocks access to it.
    – sorrell
    Feb 23, 2021 at 16:06


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