NOWHERE in the instructions does it say that the sending unit NEEDS to be grounded.

The gauge has a positive, a negative, and a connection to the sending unit.
I thought maybe it was grounded from there. ( if it needed to be )
I dunno, never done this before.

A bunch of research revealed that I am not alone here.  Other people have run into the same problem.  And the same way – nothing in the destruction’s say anything about grounding the sending unit.

Looking at pictures of other ones, they seem to have a connector for the ground wire.
So I guess they just ASSUME I should know this.
So to test it (  cause I didn’t want to drop the tank again for a 4th time ) I ran a wire to the negative on the battery, and the other end to the metal plate on the sending unit and connected it with a small magnet.   Low and behold showed up again to laugh at me, and there it was, the gauge moved.  Not much, but it moved.

So now the tank HAS to come out.
I need to attach a ground wire properly, AND figure out why the gauge is barely moving.