Magnum energy inverter? There have an on/off on the control on the unit in our 2015. I have to make sure the inverter is in the "on mode" not just passing the park power though. Before I pull out of the house I unplug the power then open the door on the refrigerator to make sure the light is on inside. If its not the inverter is off and only pass the utility power though.
On a side Note you really need a DC-DC charger to keep the battery at 100% charge. Your typical truck 7 way round can only pass about 4~5 amps due to voltage drop in the truck wireing. The best way to fix this issue is a Victron Orian smart dc-dc , basicly it takes the 12 volts at the rear plug and boost it to 14.4 volt (or what ever you set it to). Its compatable with every battery type and charge voltage needed. Mine is the 18 amp version so I was able to just use the factory plug wireing. It draws about 23 amps+- to make 18 amp at a volt that can charge the battery. Bottom line is that your 14.0vdc your truck is producing at the motor 30' to the rear of the truck is closer to 12.0 volt and that will not put much of a charge into the batterys in the coach. I installed the DC to DC charger 18" away from the battery so its at 100% SOC no mater how long we are on the road. Without it my battery would last about 10 hours with a 220 amp hour battery bank plugged into the truck and the inverter running.
Mark & Melissa
2015 Redwood RL38 , Kodiak disk brakes , 17.5" tires , 8K Morryde IS