I recently bought a trailer from Harbor Freight and can't get the lights to work. I used a tester and made sure the wiring on my 4Runner was ok and everything worked. I put the ground of the tester on the trailer ground and it seems as though that's my problem, bad ground on the trailer. I have no idea what to do to try to get a good ground! I cleaned up all the powdercoating from around the ground screw and also tried using a washer with teeth, nothing seems to work, help!