You may want to disconnect connector 13A -13B which is a 4 wire connector under the seat. Wire colors are (1) Orange/Gray,,,(2) Yellow/White,,,(3) Solid Black,,, (4) Solid Black. 13B is the side going to the float assembly. It has the metal female pins.
Take your ohm meter and measure between (3) solid black and (2) Yellow/White of 13B.
If fuel tank is full, the reading should be 7-14 ohms. An empty tank should have a 74-95 ohm resistance. A half full tank will be approximately 30-38 ohms. If you read 7-14 ohms and the tank is not full, that's your problem.
According to my information, this should be accurate. If you find the connector and the wire colors match to what's above, you should be good.