Running lights not working on CM flatbed

Buy a test light 15.00-20.00 best tool in your box for electrical issues. Gonna take a shot in the dark and say the the taillights are not grounded as the original bed was the ground point. Wire would be a small black wire w an eyelet in at the end. Use test light on each fuse till you find the one w power to one side but not other. There are I wanna say three fuse boxes one under hood, inside pass side kick panel and another drivers side kick panel (might wanna verify the last one) if they worked prior to new bed its a wire left off or came off w the bumper if unpluged from connector

**BOX**