This question already has an answer here:
I purchased a wifi thermostat and cannot located the common wire. My unit is old and is a Coleman 70 with no terminals inside labeling the wires.
As you can see in the second image, there is a blue wire that is not being used that goes to my thermostat. I am trying to use this as a common wire, I am just unable to determine where this wire connects to.
THank you for the help.