Formerly the bane of my existence. You're looking at the input jack on a 1984 Les Paul standard. They don't really make these anymore. Somewhere around 1986 Gibson figured out it was cheaper to ground the strings than it was to encase every component in a steel chassis. Replacing it would mean grounding the strings, which would mean drilling a hole. I'm rather emotionally attached to this particular guitar, so that wasn't really an option.
Thankfully, when I opened it up it was nothing more than a 1/4" jack in a chrome box.
Input was shorting out every time the cord jiggled. As you might expect, playing a guitar like that isn't something you usually do sitting still. You move around. Typically while plugged into a very large amplifier. This leads to loud noises of the non-musical variety. I'm not Thurston Moore, so this doesn't exactly work for me.
Turns out, the non-tip wire (upper right) was touching the edge of the chrome cylinder. A little electrical tape, and she sounds like a dream. Somewhat.
Sliced the living hell out of my hand putting her back together. After all that, I doubt I'll be able to play for a week.