72 water temp gauge grounding? Also questions about printed circuits

[chevy72blu]

I have a damaged printed circuit and I plan on ordering a new one. I just installed a box body voltimeter but Im having issues with the temp gauge.

About a year or so ago I managed to get my water temp sensor reading correctly by installing a ground wire between the column mount and one of the terminals. Its been a long time and I dont remember which of the 4 posts is the ground? Its tough to guess and check while fighting the oil pressure connection each time.

Also, being again that I'm working with an old hodge podge of parts, I'm missing some of the terminal nuts. Being resourceful, I pulled the lower one from the fuel gauge (unused) to use on another terminal, and this caused the fuel gauge to no longer function. I dont see anything in the printed circuit that connects there, so I'm a bit confused. Does that nut ground itself to the tin housing?

Lastly, what diameter nut are the terminal connections?

If you cant tell I'm electrically 'tarded and its been years since I wrenched on one of these things. Thanks for the help!