Thought I would get this out here on the forum for others who may run into this.
During my restoration I replaced the fuel gauge with a tack and installed a new center fuel gauge. When I got the car wired and on the road I noticed the fuel gauge read way over full when full and stayed there for a long period of time. Once it started to drop it dropped fast and when it read 1/8 tank I could only put approx 12 gal in.
The sender worked fine (0-93 ohm sweep) and the gauge would read E when the sending unit was was grounded as it should.
There are a number of sites that show how to wire, test, troubleshoot the gauge but nothing quite matched my symptoms.
something got my attention and the light went on......Newer/replacement gauges are internally resisted where as the factory gauges required the resistor/shunt between the 12V pos terminal and the sending unit terminal. I had installed the resistor/shunt from my factory gauge onto the new OER (or Classic Headquarters) replacement gauge which is wrong - its not needed since the new gauge is internally resisted.
Rather than remove the dash and cluster I simply reached up from the bottom and ran a razor knife across the back of this wire wound resistor/shunt effectively opening the circuit. Once this was done the gauge immediately went to Full vs. way over full which was expected since I had just filled up. Everything works as expected now.
For the electrical nerds....90 ohms of resistance from the sending unit (full tank) + the 84ohm resistor/shunt = 174 ohms resulting in the needle going way past full.