thank you in advance. I have been struggling to find a proper way to install my ecobee. It is again 'C wire' issue. My old thermostat uses 4 wires (red, yellow, green, white) and does not use c wire. I am attaching the wire diagram and the picture of wire connections.
I am suspecting the brown wire (which is not connected anywhere) is the common wire but not sure. I have a multimeter but am not sure where to connect to check 24 AC. That is, if I connect one line of multimeter to brown wire, then where should I connect the other line of multimeter to?