another fuel gauge issue

Yep, needs to be grounded. That is EXACTLY why I recommend ADDING a ground wire in my post above. You either need to solder a wire to one of the board ground traces, or install one under a screw and make SURE it is clean and tight. Leave it long enough, about a foot or a little more, that you can bolt it to the column support before you put the cluster clear in.

(You actually don't need the ground for the gauges, you need it for the voltage limiter)