Please take a look at this explanation I wrote up a while ago: https://tinyurl.com/mr2xspy7

As Kevin pointed out, you may damage the sender (not the gauge) by reversing the wires and putting battery voltage on the sender terminal. The good news is that isn't a promise. Let's for right now hope that didn't happen. What I wrote should explain the working of the gauge, sender, etc. At ignition off, your needle will go to empty. Please also keep always in mind that your sender unit is a variable resistance thing. That's all it does...the unit provides between 0 and 30 ohms resistance to ground. Let's start with what I've written and go from there. If you need to catch me directly, use [email protected]

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end