HELP! 12 volt Breaker in Travelmaster 1987

Whoah! Thanks a whole lot for your answers guys! That's a lot of things to verify! I will follow all of your advices and get a voltmeter/multimeter. But to answer a few of your questions:when I first bought the motorhome, everything was in order. The heater would function fine on my auxilliary (deep charge) battery wich is brand new. I have had to recharge it recently, because the heater and the hot water tank drain a lot of power.I occasionally get a chance to go to a camping where I can plug everything, and I would get the luxury of having heat and hot water. The circuit have shut down recently.I still have my ceiling lights and water pump functioning, so that's why I suspect a faulty circuit rather than a discharged battery. I looked for the GCFI outlet; I do have one in the bathroom area, but it doesn't have any reset button on it. I'll check the converter, which seems to be under my bed... maybe one of my puppies ate a wwire under the dash... you know how puppies are! So lots of homework for me to do, and I suspect lots more questions for you all. Thanks again! (And thank god for my Coleman Mr. Heater!)