Reply to Doug Rainer
1. Front unit was replaced 2 years ago with a "temporary" one. Back unit was 20 years old. Going with new heat pumps and new thermostat.
2. Used new dometic supplied cables.
3. Connected to the connector box at the end of the short cables with the unit. 1 to thermostat 1 to 2nd unit.
4. Ran a temporary cable across the floor to test it. Old cable was damaged somewhere as there was no 12v coming through it. I will run the new cable through the vents. I am aware of the ends needing to be the right way.
5. Didn't use any of the old parts. New units have built in control boxes.
Any assistance is greatly appreciated