It's probably a small wall switch on your truck camper. It would be on the wall somewhere, probably in the kitchen area and possibly on the side cabinet walls to the kitchen area. If it isn't there, then it is probably back in the back near the entry door, on the wall on one side of the door.
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR