[Roadsters] fuel gauge troubleshooting

[Krismon ongbongan]

any tips on troubleshooting the fuel gauge on my '69.

background:
oil pressure, temp gauge works.. ammeter is unhooked (presumably from a
motor swap years ago).
It did "work" when I got the car earlier this year.. a Full tank showed as
1/4, now the needle doesn't even move... swapped out a voltage regulator a
couple of months back (with one from a 510) when the temp gauge & oil
pressure stopped moving.. but fuel gauge never came back.
I did have the tank pulled out to be refurbished this past spring, too...

So..now the question.. how do I tell whether it's the sender or the gauge?
easy way to probe with a multimeter?

Kris.