[Seeker]

The service manual says if you disconnect the fuel pump coupler and connect a variable resistor between the r/b and b/w pins on the harness side you can check the display with ign on.
200Ω = low fuel blinking + 1st bar blink (you've just run out of fuel!)
148.9Ω = low fuel blink
69.2Ω = mid range
14.9Ω = full
It takes 40 secs for gauge to read correctly

If you don't have a variable resistor/pot any fixed value between 15Ω and and, say, 120Ω would tell you if it's a sender or a gauge fault since you should be getting a static display.