OK....Here is my story, and I appreciate any advice in advance.

The left side of my trailer lights were not working. (1) I checked the ground on the light, scuffed up the connection, and did the same with the ground at the ball. Nothing. (2) I took a volt meter to the plugin the goes directly to my light. I got a reading of about 10.5 or so. (3) I took the light and switched it over to the right side, where everything is working fine, and the light worked. Everything I read said 99% of trailer issues is a bad ground. The only grounds there are, are the grounds at the lights and at the ball correct? I have been so stumped that I (4) ran a whole new trailer wiring kit, and the ground at the ball used to be wedged between an old rusty bolt, so I inserted a self tapping screw right into the trailer this time. After the whole new trailer wiring, I put the keys in the car, and BAM, the same exact result. I am completely stumped.