Got a bit of an odd one with the fuel gauge on my AKS400, when it's full the gauge reads full, when it is totally dry the gauge reads just to the lower side of the half full dot, I discovered this driving to work this morning! My understanding wife came to the rescue with a 10L can of fuel, which I poured in and the gauge went up to a smidgen under 3/4 full, stopped at a petrol station brimmed the tank, & It is back too reading full. linearly the gauge appears to work about right all be it only in the top half of the gauge? Being that the sender unit is basically a variable resistor with full position giving a low resistance and therefore a high gauge needle deflection & empty a high resistance an therefore a small needle deflection It seems odd that it seems to give too low resistance at it's lowest point, any king of degradation, tends to increase resistance?
My only thought but I'm stretching my electronics knowledge here Is could it be a sender unit from a 6v vehicle paired up with a 12v gauge? Know idea if that could even cause that? Just aware that something odd is happening. Would be grateful for anyone's musings on this who understands this more than I
It drops to nothing when the ignition is off

You need to take the sender out of the tank - I suspect that the contactor is either damaged or sticking on the windings - they tend to wear out the end of the contactor where it goes against the windings on the resistor and I suspect it stopping short of the bottom - they can be resurrected by judicious application of solder

Surely if the contactor was worn it would tend to read low? not high? Also if it's stuck short of the bottom, that was my first thought, how dose it read 3/4 full with only 10L of fuel? that wouldn't reach the float stuck at half way