The + and - are data wires for a communicating thermostat that talks to the furnace.
To use a Nest or any other standard thermostat you would need to go to the equipment and move the wires over to the terminal strip that has the standard labels on each screw. Such as Y G W R C. And also on the outside unit you would have to move the wires.
If you take the cover off the indoor unit there is usually a decal with wiring diagram showing the thermostat wiring for communicating and standard thermostats.
My one question: If I have a Lennox HVAC that is using their thermostat, can I change it over to a Google Nest Learning thermostat and have fun functionality of my Lennox HVAC? The reason I am asking is two fold: 1) I heard the thermostat I have now does tend to malfunction over time; and 2) I read that the Google Nest Learning Thermostat cannot give fun functionality to the Lennox HVAC. Thanks.
@Georgerb, just one quick final check in here since activity has slowed down. We'll be locking the thread in the next 24 hours, but if you still need help, we would be happy to keep it open. If there's more we can do, just let us know.
I appreciate the help, Houptee, Mark, Edward and Jake.