My 2000 Magna has a 15 amp breaker in the breaker panel in the bedroom. There is a switch in the driver's left armrest also. I've never turned the block heater on but assume I would have to turn the breaker on and then turn on the switch on the armrest. I will add that if I turn on the Hurricane furnace, the engine temperature will get up to about 105 degrees so If I run the Hurricane I see no need for the block heater.
Pete - Full Timing
2000 Country Coach Magna 40' Indulgence, CAT C10, #5892
2019 Ford Ranger XLT