Also, you seem to have it in your head, "why does the speedometer work?" It isn't electric, it doesn't have anything to do with the fuel gauge. It's mechanical, and totally separate.
Thanks. I am not really hung up on the speedo, it was just mentioned previously. Since it is cable actuated, I figured it doesn't have anything to do with the immediate problem. I assume there must be a ground issue since all of the cluster lights do not work as well as the two gauges. Going to also go back and check the bulkhead connector as well.
I really appreciate all of the insight from everybody. I can work through body and mechanical stuff, but electrical issues are way beyond my usual skill level. But I did spring for a service manual, so hopefully that will help.