I'm on the road and doing this on my iPhone so if there is any misspelling that I don't catch, please bear with me.

Good. Now we know that there is no current flowing through the circuit. This is NOT a shorted wire; rather, it is an open circuit.

The following simple test will isolate the problem to one of 3 areas: power, gauge or control (tank unit segment).

Test for power on both posts of the fuel gauge. Simply put one test lead to one post of the gauge, the other lead to a good ground. You'll find it may be anywhere between 0 and 12 volts, depending on whether your temp gauge is also operating, because of the voltage regulator unit. Also remember that the "regulator" is really just a betallic switch that turns the 12v on and off, so it generally averages about 12v. Make sure you connect your voltmeter and watch it for several seconds each time to allow for the switching of the regulator. Remember to chech power on both termonals of the gauge.

So here's the next question: Did you find power on both posts, one post, or neither post of the gauge?

(If this is too basic, please say so but I have no idea what your skill level is.)

If you have no voltage on either post, you have a problem with the circuit providing power to the gauge.

If you have voltage on one post but not the other, you have an open circuit in the gauge (bad gauge).

If you have voltage on both posts of the gauge, you have an open circuit between the gauge and the ground after the tank unit.

Post back with the results and we'll work step 3.