If you have power there, then yes it's a bad ground, providing your bulb is good. Since the previous owner spliced into that side for his trailer lights, I would check there first, especially if he used scotch locks or some kind of quick connects.i have already replaced it once, it seems to be just the middle bulb, do you think it could be a bad ground? Previous owner spliced into that side of the truck for trailer lights. Thanks for the info , Mike L