It looks like a small box with two terminals on it. (see photos)
On a travel trailer it is under the frame and on a 5th wheel it is located under the pin box (in mine). There is another located in line before that close to the battery, but because your slides work, that one is good.
Look for corrosion at the terminal or a popped reset button located on the side.
Lou, Laura, & Freya the wonder dog
2008 GMC Sierra 3000HD Crewcab SB Allison Duramax
2019 Flagstaff 8529FLS - Pullrite 3300
HAM CALLSIGN - KC3FFW