I can't see the picture Pepi posted (it says that an additional program & decompressor are required to open the picture in the MSWord file), but one thing that jumped out at me reading Pepi's post is Don's statement
I ran 2 wires(one from the sending unit terminal & one from the sending unit ground) to the gauge. There is also a hot wire from ign to gauge.
As pointed out the ground connection at the gauge and the ground connection at the tank are not to be connected together via insulated wire, but are a chassis ground to complete the circuit from the ignition power, out through the sending unit and back to the gauge input. If you simply connect the gauge (-) to the sending unit (-) you have no ground with the poly tank, right?