Don, if your diagnosis points you to the fuel sender, I can tell you
that on my car empty is about 23 ohms and full is about 160 ohms
although this is from memory (I wrote them down but they are at home,
let me know if you need them and I will get them for you), and of course
YMMV. I read these resistance numbers with a DMM by disconnecting the
sender unit wire at the fuel gauge. If you don't get close to these
values, you probably want to suspect the sender or a bad ground. If you
have a resistance substitution box or want to buy some cheap resistors
from Radio Shack, you can simulate what the sender unit does and see if
your gauge and voltage stabilizer is ok.
The gauge itself has an adjustment for zero and another adjustment for
overall range to full but since your problem sounds like it happened
suddenly, I doubt this will fix your problem. Probably a bad ground,
the voltage stabilizer, or the sender unit.
After running out of gas for the second time I figure it's time to
tackle the fuel gauge in my 72 TR6. Empty still reads between an eighth
and a quarter. Half full reads full. This is a recent phenomenon. Can
this be dirty grounds or what?