I'm trying to connect the C wire in my Goodman furnace in order to install a new thermostat. I've read all the posts on this forum about this specific issue so my question is whether i'm in the right path or not. Here are a couple pictures of my transformer and the R G W Y and C terminals. Transformer As you can see, on the lower left side of the transformer I have two blue wires and one wire connected to the chasis. From what I understood from other posts, one alternative is to use a piggyback connector to link it to the C terminal.

Terminals I don't know if you can appreciate it on the picture but the C terminal is on the bottom and there's a blue wire connected to it that's also connected to the chasis.

So, to sum up my question is: do I have to use the piggyback connector or being both points connected to the chasis the only thing I have to do is connect the thermostat to that C terminal?

Thanks in advance

1 Answer 1


You should be able to use that screw terminal for the C wire in the bottom picture. I assume that the blue wire on the spade terminal goes to the 24v transformer? It looks like the transformer has a red wire and a blue wire coming off it. The red wire from the transformer is the "R" and the blue wire would then be the "C" wire.

Looks like an easy hookup - on some older units to have to hunt around more to find a good connection point.

  • Actually that blue wire is connected to the chasis as is also the dark cable that comes out of the 24v transformer, that's where I got kinda lost.
    – Patuno
    Jun 26, 2019 at 12:38
  • The “common” side of the transformer being attached to the chassis is pretty common.
    – JPhi1618
    Jun 26, 2019 at 14:38
  • But the fact that the blue wire from the C terminal is also connected to the chasis means I have 24v on the C terminal? Thanks
    – Patuno
    Jun 26, 2019 at 20:16
  • Yes, if you measure between red and blue, or red and the chassis, you should have around 24v.
    – JPhi1618
    Jun 26, 2019 at 20:18
  • Hi, I just wanted to let you know that it worked! Thanks for your help.
    – Patuno
    Jun 27, 2019 at 20:24

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