All major components on a boat should be electrically bonded
together. This is especially important to human safety. Your gas tank
is electrically floating? Then it is a situtatoin similar to what
destroyed a 707 over Elkton MD. That is dangerous. Gas tank should
be grounded using a 10 AWG (or heavier) ground wire so that engine,
tank, and all other major metal components are bonded electrically and
so that bonding makes a connection to water.

A discussion of this concept:
http://www.thomson.ece.ufl.edu/lightning/ Summary
http://www.thomson.ece.ufl.edu/lightning/IEEE.pdf IEEE paper
http://www.thomson.ece.ufl.edu/lightning/video.html Video

Apparently that gas gauge problem is but a symptom of a more
dangerous and serioius problem.

bobk123 wrote:
I bought a 1996 sea ray f-16 jet boat last summer and the seller said
the engine had recently been rebuilt. I noticed that the fuel gauge
did not work when I bought the boat so this week I decided to replace
both the fuel level sender in the tank and the fuel gauge. The new
fuel gauge still does not work. In trying to figure out why the gauge
does not work, I noticed the fuel tank had a green wire attached to it
and the other end of the green wire was connected to the engine block
at the same point where the battery +12 volt line is connected to the
input of the starter solenoid. Because of this, the fuel tank is
always +12 volts. I verified this with a volt meter that the tank is
+12 Volts. This is apparently why the fuel sender is not working since
their is no ground for the sensor. My question is this. Should I
disconnect the green wire from the input to starter solenoid where the
+12 V line is attached, and connect the green wire to where the battery
negative black wire is connected on the engine block? I'm assuming
that when the engine was put back into the boat someone connected the
green wire in the wrong place. The boat worked fine all summer so the
tank at +12 volts did not cause any problems other than the fuel gauge
malfunction. Thanks for your help.