Whether you're installing a regular or smart thermostat, don't forget to turn off the air conditioning and furnace units before making any changes. If electrical wiring systems stress you out, hire a home service pro instead to get the job done.
Mark checked on the electrical wiring relating to the furnaces to insure that the furnaces are functioning efficiently with respect to one another.
Minor adjustments were made and both furnaces are functioning properly.
Kale suggested that the wiring should be examined by...