It sounds like a little automotive indicator light that a prior owner installed possibly to show on the outside that something was left on. What color is the jewel part? Have you tried easy the thing out? If it's the kind of light that I'm thinking of, it should pop out. Post a photo of if you can.
SuEllyn & Brian McCabe
WBCCI #3628 -- AIR #14872 -- TAC #FL-7
2015 FC 25' FB (Lucy) with HAHA
2005 Suburban 2500 Quadrasteer (Olivia) & 2011 Silverado 3500 (Fred) with Outfitter Truck Camper (Ethel)