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