[Trainer]

Morning Rick, The red wire that is joined to the black wire on the C-plug is connected to the bottom conection of the center relay. It is called the "Diode Wire".

Its purpose is to run the center zone pump anytime the burner motor is running which stirs the coolant tank providing uniform temp to the coolant, no hot and cold spots. The diode prvents the center relay from back feeding power to the C-plug when the center relay is running the center pump and the fan coils in the center of the coach for interior heating.

I cut the red diode wire and install pull apart connectors so as to have more slack when removing the burner for service. If your red wire is not continous, please install a connector.

Hope this helps you all.