Better would be to connect the sending unit wire to one side of a resistor. Ground the othe side of the resistor.
10 to 75 ohms will work. around 23 ohms should get the gage to indicate half full.
Its better to use a resistor because direct grounding can quickly burn out the gage.
Thank you for explaining how to diagnose. I am a HVAC tech working overtime on call but as soon as I have time, I will do this test. Thank you so much.
