So I just got finished with my second physics course (electricity and magnetism) and from what I learned about circuits, to complete a circuit there must be a potential difference to create a current. I just wired up some new off road lights on my vehicle, and when wiring, I ran a wire from the positive terminal of my battery to each light, but had a ground wire on each that I just bolted up to the frame (no return wire to the battery). Can someone explain to me how this works? Do the electrons flow through the battery, through the lights to the frame, and eventually to earth where the potential is 0, thus creating a potential difference? Why don't I have to run a return wire? What exactly is the difference between a ground and a negative terminal on a battery?