Fuel Gauge is Fluctuating Badly?

1987 SN2001, When I fill up the tank the gauge reads full like it should, after a couple pulls and the gas level starts to go down the gauge starts acting nuts. It just goes up and down through the whole range of the gauge sporadically and never stops moving even if the boat is sitting still at the dock. Thoughts??? The gauge? Sending Unit in the tank?

Thanks! Now I wonder if I can fanangle it out of there without removing the gas tank since it's pretty much full and it's already winterized....

One quick test though:

Remove your red/pink wire from the center, and ground it directly onto the metal ring, or touch it/connect it to the same place as your black ground wire.

If the gauge pegs steady to full, with no fluctuation, that's a pretty sure sign your sender is the issue.

The problem with that is the tank is full so it's reading full, that's the only function it does properly. Lol

On my old ocean boat the fuel sender was constantly causing issues. I replaced it with a Centroid capacitance sensor. They work great. The only issue is that that don't work with all gauges.

http://www.centroidproducts.com/

There are no moving parts. It wires in like the stock sensor (2-wire version). The cool part is that there are two pots on the sensor. You can adjust the full and empty levels. If you want the tank to read empty at a 1/4 tank you can. That way you can fake a reserve. All you have to do is give them the depth of the tank and they will make it any length you want. Mine was bullet proof for years.

Chuck