My dad has a 96 cummins that is all stock. The plug to plug in the trailer has a problem. Everything works except the trailer charge that is used to charge the RV's batteries. He has one that is in the bed and the other that is on the bumper. I have checked under the hood and switched relays, tested fuses and made sure I was getting power to the fuses and relays. He has no trailer brake in the truck but will soon get one. I was wondering if that has something to do with it. I have also pulled the plugs to make sure no wires are loose. Has anyone else had this problem?