I'm trying to connect up a wifi thermostat to Goodman furnace, specifically the GMP050-3.

I've done some reading on this but I'm still not quite sure how to go about it. Specifically, I'm not sure how (or if) I can find a substitute for the C wire on my wifi thermostat. Thanks.

Schematic: enter image description here

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And here are photos of the actual furnace wiring: enter image description here enter image description here enter image description here


  • Can you post a photo of where the existing thermostat cable connects to the furnace wiring? Aug 19, 2018 at 0:15

2 Answers 2


Looks like you are not the first person with this furnace. If you have air conditioning then... http://www.dslreports.com/forum/r28226387-goodman-GMP050-3-Gas-Furnace-where-to-find-24vac If not then do you have a voltmeter? You are looking for constant 24 volts a.c.. Might be that BL wire that connects to the C1 terminal. Check between there and the R terminal.


One of the terminals of the transformer has 3 blue wires attached. Use that terminal as the "C" terminal.

  • 2
    It may not be clear to the OP how one would do that.... Apr 28, 2020 at 23:12
  • Could you expand on that ? Use edit to add details.
    – Criggie
    Apr 29, 2020 at 2:26

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