by droopsnoot » Sat Jul 17, 2021 6:01 pm
The fuel tank sender is a variable resistance, or rheostat, which provides a variable resistance to earth, similar to how the temperature gauge does, albeit in a different way. You have 12v on one side of the gauge, and the sender varies the earth by moving the rheostat "pointer" on the coil inside the sender body as the float moves up and down. At maximum fuel height, the resistance will be at its minimum and allow the gauge to read high. At minimum height, the resistance will be maximum and give a lower reading. Basically it's a voltmeter, and the sender varies the reading by altering the earth.
To test it, read the resistance from the body to the terminal with the float at either end of the scale. I don't know the resistance range on a HB sender - I'm not sure I remember it for HC, for that matter.