Same Problem on NTM 2014 FS 206 LTD
Lights would sometimes work, Heater would cycle once, and not re-light and cycle. The previous owner provide a small auto type battery, 450A, Hooked up a 15A battery charger to that battery no change.
Connected the 7 pin connector to my car, heater came back on and cycled, Light works every time.
Replaced the wimpy battery with a deep cycle/marine battery and was able to run for at least 6 hours, driveway camping and weather stopped the test.
Lesson do not use a wimpy auto battery.