Fuel level sender wiring diagram needed

[Reel Thing]

1992 Proline 238 Center Console with dual Yamaha 130 2 strokes

I replaced the sending unit last year. It seemed to work but didn't seem accurate and sometimes wouldn't register at all on the gauge.

When empty the last bar of the gauge flashes.
Here is the gauge:

When I ground the wht/blu wire on the back of the gauge, it reads full.
At all other times, no gauge at all.

:facepalm:
So I am planning on running all new wires to the sending unit.

What have I done?
I put a new terminal on the green wire and connected it to the tank ground. This made no difference.
I checked continuity between the S & - posts on the sending unit with all wiring removed. The reading was 204 which means I should have less than a 1/4 tank of fuel left. (130 gallons full)
I ran a ground wire from the battery to the tank ground. This made no difference.
I connected the ground to the - post with the other black wire still attached. No difference.
I removed the original black wire and left the new ground. No difference.
I left the ground connected to the - post and ran a new wire from the S to the wht/blu wire on the back of the gauge. No difference.

So I am stumped on how this simple gauge actually works.
What should the sending unit be wired to?

 

[Reel Thing]

Re: Fuel level sender wiring diagram needed

Spent all weekend on 3 stupid wires. Turns out I had a bad pink wire, a black wire that was actually pulling voltage from somewhere and a tank ground that had a bad terminal too. So I ran a new ground wire, hooked it up to the S pole. I fixed the pink wire (wires had rusted and broken free of a butt connector under the helm). I connected it between the Wht/Blu on the gauge and the - pole.

I thought that the pink wire would have gone to the S pole and the ground to the - pole but when it started working, I stopped fiddling. I still need to solder and shrink tube all of my connectors next weekend. I'll swap the pink and ground wires then and see if it still works. I'll also update my drawing for future reference.