72 F250 tail light issue

[Fordguy85]

so I'm pretty sure this is a ground issue, But here is the deal my driver side tail light/brake light does not work, however the turn signal does work, the passenger side is the exact opposite. when i take everything apart and move it around everything works if i get it in a certain position. so my question is do you guys think its more than a ground issue ? and what gauge is the wire ??