I would not count on the ground being the best going through the ball.. Many wiring issues are caused by bad grounds on trailers, and with the amperage that a 4gauge wire can hold things will be getting hot FAST. The plug I showed you is not affected much by weather and carries both the ground and hot leads. You bolt the ground leads to the frame of the truck and the trailer and have a bullet proof ground at that point. The 150 amp fuse is only for overload protection, If you blow it something BAD happened but prevented a fire that a dead shoted 4gause wire WILL cause.