You might have a battery disconnect switch. Start at the battery(s) and battery box. this is a good time to locate your breaker or fuse that is usually right in that area so you can replace it if it blows. then trace back into the camper and see if one is mounted anywhere up to the main power breaker/fuse box. then go online and order one that you like. Lots of searchable advice above in the gold bar, search battery disconnect.
I got one of these as it is 100% simple and positive, the first one that rotated died after a few uses.