i've had a similar problem and i found the solution.
in the back of the gauge, where the 2 coils are located, there are very tiny copper wires which connect all the resistors/diodes. they each travel from within the coil and are soldered to 3 out of the 4 mounting pins. if any of these wires are shorting out or disconnected, the gauge will malfunction.

-take the gauge and flip upside down
-temp gauge has 1 resistor (blue) and 1 diode (copper)
-fuel gauge has 2 resistors, no diodes
-1 wire should be attached to bottom mounting pin (letter E for EMPTY)
-1 wire should be attached to pin holding both resistors (half tank)
-1 wire should be attached to the stand-alone ground pin (no mounting bracket)

hope that helps!
good luck!