Yes, buy a HF meter, very cheap and useful. Suggestions given are good.
You will notice in the trunk, bottom of the structure holding the latch, a tan wire.
This wire goes to the sending unit.
Disconnect the connector and measure in refence to ground, black lead, and red lead onto wire through floor, and read s/unit ohms.
Anything between 0-90 ohms, 0 = empty, 90 = full.
You can also get a resistor, 45-50 ohm, and attach one lead to ground, the resistor lead to tan wire into body, and gauge should read approximately half full/empty.
Tank capacity is 16 gallons. Good luck.