Brake light problems!

[Mick65]

My brake lights are whooping my butt right now. I'm all out of ideas. When my headlights are off the right brake light works just fine but the lefts running light and break light are much more dim. When I turn my headlights on the running light/brake light on the right remains to work just fine but the running light on the left remains dim. When I hit the brakes with the headlights on the light on the left completely goes out. No running light or brake light.

The entire silver housing on the left reads hot when touched with a voltage reader. Would this be a ground problem? If so, why would it only effect one side? There is a factory ground on that side of the truck from the bed to frame. Would replacing this ground help?

Thank you everybody.