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I believe it's a sending unit issue, but trying to verify before I replace the unit. Here's the issue...................
Fuel gauge reads full with a full tank. (31 gal) As fuel is consumed, the gauge will eventually drop to the 3/4 mark and that is where it stops. When the switch is turned off, gauge returns to E. Switch on, back to the 3/4 mark. Unless I fill the tank again, then it's back to F and the process starts again. The gauge does register correctly between the F and 3/4 mark before it stops at the 3/4. Today I pulled the unit and worked the float manually with the same results as if it were in the tank. Switch off, gauge to E. Switch on, works fine between 3/4 and F. Replaced the connectors and checked the wiring. My guess is with the gauge actually moving with the switch on or off, and working correctly between the 3/4 and F, the problem is the sending unit. Am I thinking correctly or not. Any thoughts and thanks in advance for the input.
Boat is not that old..........2004.

You are correct sir, it is a sending unit problem. The sending unit works on a variable resistor. As the float moves up and down it moves a contact across a resistor that is painted on a ceramic plate. if there is a spot worn out or the contacter does not touch in certain areas it will not read correctly. Replace the sending unit.
FF

Take your wire off the sending unit. The gauge ( with the ign. switched on ) should go to full or empty. Ground the wire and the gauge should go all the way the other way.

Thanks for the info. One more test this weekend should confirm.

Just installed the new one..................back in business.