its probable the oem unit was a 'heat pump'
it was the primary heating source, and the furnance was secondary and came on if/when the heat pump could not provide the needed amount of heat
the fire probably destroyed the wiring, but if you can find the thermostat control wires and connect the correct wire back together, the furnace should work
OR just run new 'stat' wires
do some reasearch find out what 'heat pump' is normal for that RV
visit an owners group and ask questions about the heat pump operation and wiring
look up the MFG specs and wiring diagrams for the heat pump
