If this is a ceiling light you might want to check if there is also a switch by the front entry door. My ceiling light has a switch by the front door and also a switch on the fixture itself. the entry switch by the door has to be ON before the fixture switch will work. Check it out, might be the problem. If it is the problem, the proper way to use such a system is always control the light by the door switch off and on and leave the fixture switch in the ON position so you can turn the light ON when you enter the RV instead of fumbleing around in the dark for a switch on the fixture.