Fuel gauges on the Carver 390 CPMY

My fuel gauge switches don't turn but rather rock for and aft. Press forward and it shows tank level release and it springs back to neutral position.

Spent a very frustrating day yesterday trying to figure out why port fuel tank is not "gauging". Found the sender on the port tank, so, yes, it is supposed to be guaged. Traced wiring to the "connector" behind the cupboards and also pulled the rocker switch out from the panel for ease of testing. Pulled apart the connector and noticed that all 3 wires had vertigris on them so decided to replace that connector with a clean connector. Used ohm meter to determine which wire is from the port sender (L1). Used the ohm meter to determine that the rocker switch was working properly. The guage works to show the stbd side fuel tank level so guage is OK. So...I pulled the sending unit out of the tank and tested it with an ohm meter (260 ohms at empty position and about 55 ohms at full position) which seems to me to be working. Checked the integrity of the float itself and it is OK. So why the hell is this not registering on the stbd side guage when I depress the rocker switch to the port-aux position (yes, I did turn the ignition key on, both sides just to make sure nothing screwy going on there)? At my wits end with this. Any advice appreciated. As a last resort I am going to replace the sender in the tank. If I still have no success, I guess I will have a spare sending unit and I will be back here to see if any of your comments reveal something that I have failed to check. One thing did occur to me during my restless sleep that I didn't check, and that was to make sure that the aluminum tank is actually grounded. The sender has to 2 posts on top, on goes to the rocker switch, the other grounds to the tank top. I didn't try reversing these wires (should I?). Any ideas???

I will try that again if I already hadn't. I tried so many things yesterday I may have already. I will do that when I pull the sender out and manipulate the float.

Mystery finally solved. Turns out that the ground wire for the aluminum tank itself, not the one from the sender, had a corroded connection, visually it still looked like a good connection but when I put a wrench on the screw holding it down to the tank, it spun freely and pulled out with ease. There was a thick coating of corrosion on the screw threads preventing contact between the wire terminals and the tank. Once this was corrected, the sender started working again.