at the sensor, ground the pink wire ,use a wire connected to the - battery NOT THE TANK GROUND at this time.
gauge should read full, now do the same test with the tank ground, should go full also.
If it does not show full, use the ground from the - battery at the gauge and short the S of the gauge to ground, gauge should read full.
These should cover it. ***
Sure wish we could get those in a sticky as they have been posted 100 times and the Teleflex diagnostic link in the Mechanical How-to Articles Forum as been dead for years since Teleflex Marine dropped diagnostic info and sold the analog gauge division to India(?). .