I purchased a used King Saltwater trailer this winter and when I back up (usually up a hill) the brakes are locking up on me. I understand the basics, like when the pin is pushed when I put the breaks on my truck, it activates the brakes on the trailer. Am I missing something here? There is a wire that's not plugged in, but I have no connection on my truck for it. Backing down a hill/ramp is no problem. I included some pics of the front end of the trailer.