Assuming you have the heavy duty tow package, the trailer plug wiring has its own isolated relay isolated circuit and fuse protection. This is a very nice feature as you just found out that you only blew a fuse on the the trailer lights and didn't loose all your turn signals on your vehicle. Look at the wiring diagram that is with your brake wring pig-tail (check by your tire tools & jack) for the relay & fuse info. You should not rely on the trailer ball for a ground. Use a multimeter to check for shorts to ground on the trailer wiring.