That light is above the door that allows access to your battery. Open the front bay doors, look up there, and make sure wires going to the light are attached.
I know stranger things have happened, but you also might plug your camper into your truck and see if the light works. Although it should work like any other outside light, it's possible it got wired incorrectly and is active only when you are plugged into your truck (like your running lights). It's NOT suppose to be that way, but it takes nothing to check it. If that's the problem, then some new rewiring may be in order.
I'd check that first before tearing into anything else or replacing parts.
2019 Montana High Country 375FL
2014 Chevy Silverado Duramax, 6.6L Dually