G'Day 70Cuda,
I'm no expert specially not with wiring,but hey i'll give it a shot.
All they mean by grounding the tank is simply a earth wire running from the tank(i think the sender) to a good earth like the rail or somewhere similar.Pretty sure the one on my Val runs back into the boot.Make sure were you ground it is clean of paint and stuff.
Another prob i got with mine was after painting the tank i did'nt put the metal strap that joins the tank pipe to the fuel line, back on
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This was causing the tank to constanly read full or empty,can't remember.
Like i said i'm no expert,just relate what happens to me,hope it helps
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