The running lights all work fine, but when I apply the brake, the left light does not work. I replaced the bulb, and even the socket, only after which, I put a voltage meter on it, to see there was no juice going to one of the terminals. The right brake light, and the 3rd light in the window work fine, only the left is the issue.

Ground wire? If so where does it connect to body? Thanks for reading, hope you can help!