I am installing a new Ecobee Smart Thermostat. My old thermostat didn't use the C-Wire. However, when I pulled the cable out of the wall their is a blue wire. I hooked it to the Ecobee but it didn't power up. I figured it wasn't hooked up on the furnace control board.

My furnace is a Bryant Model 582ANW024060aaad. It's an outdoor unit with Ac/heat. I know the common wire is usually blue but mine seems to be brown. On my control board (LH33WP003A) what I believe to be "C" has a brown cable running to the 24V box above it. It splits off and has a wire nut on it but it's not connected with any other cables. The cables next to the brown cable run from my inside my house to the thermostat.

The following cables are connected by a wire nut (see images) Blue & Yellow - Green & Green - Red & Red - Black & White - Brown

Should I hook up the brown cable to the yellow and blue cables with a wire nut? Will this give me power for my thermostat? I included a link to the PDF of the control board schematics.

Any help is appreciated.

Control Board LH33WP003A

C-Wire Slot?

24V Box

Thermostat Cables From House

Brown Wire

Thermostat Cables

Cables Blue and Yellow

Control Board Schematics

1 Answer 1


This is your "C" wire:


  • Just because it's labeled "common"? ;)
    – FreeMan
    Dec 1, 2022 at 13:28
  • Mainly because it's labelled "C" on the PL2 connector.
    – jwh20
    Dec 1, 2022 at 14:35
  • Yeah, or that one...
    – FreeMan
    Dec 1, 2022 at 15:18
  • Thank you. So my Brown wire is the common wire. I'm assuming that's what BRN stands for
    – denp02
    Dec 2, 2022 at 11:29
  • Don't rely on the colors, rely on the terminal that the wire is hooked to.
    – jwh20
    Dec 2, 2022 at 11:32

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