RVing Drives Me Nuts ---- Electrical Issue

Please forgive my ignorance, but I am an electrical illiterate. I went back to the 5er and tried all the suggestions I had received at that point. More came in later, and I hope to go back again today. (little under the weather) My latest question.....is it possible, the ground wire in the power cord is itself grounded to the pin box itself? This may be the ultimate in stupid questions, but I want to eliminate all possibilities before I tear into the light fixture itself. One of the problems I am having in locating a ground wire is, the trlr is an All Season so no access from underneath. Thanks again for your help and patience.