I think most Beneteau
boats are fitted with VDO lever arm type level senders.
Been having problems with my one, and removed from the tank. Checking with a meter between the two contacts it showed open circuit.
Have removed the float unit from tank and looks like a connection is missing. Between the sweep arm and it's connector I get a continuity, but between the resistor bridge (not sure that is the correct term) and its connector, no continuity.
On close inspection
I can see a solder blob, but nothing in it, so I soldered in a wire to make a connection.
Now I get a resistance range of about 10 to 200 ohms which looks about right.
indicates that US level senders have a range of
240 ohms Empty, 103 ohms half, and 33 ohms full
10 ohms empty, 95 ohms half, and 180 ohms full.
Of course, with the tank shape, the sender will only measure liquid height at the place where the sender is sited, and not volume.
The VDO senders have two adjustments to allow for tank height, have attached the installation
instructions which includes a table of what these adjustments are.
Also, a good clean of the unit itself will help.
In trying to trouble shoot the problems with my sender, I came across this type
SSS/SSL Diesel, Fuel or Water Level Sensor (4 - 60 in.)
which looks a lot more robust than the VDO type, and more suitable for a boat than the lever arm type.