I checked out a fuel tank transmitter the other day.

Under an inspection panel, a single screw terminal connects a wire to
the guage from a rheostat hooked to a float. I clipped a test lead on
the transmitter terminal, and grounded the other end. The gauge read
FULL (as it should)
So the gauge was OK.

So I was all fired up to find another transmitter ($$$) when I ran into
an A&P.
He said, check the transmitter grounding first.
It took me a little while to see the value of the suggestion.
Then I realized: when a transmitter reads short, meaning tank full,
the indication can fail if the short isn't produced in the transmitter
OR the short doesn't get from the transmitter body, to the airframe.
Neat!

Brian W