I just got done fixing one of my MEP-803A's that was randomly pegging the fuel gauge all the way to the left.
It was pegged down when I bought it, so I swapped in a known good gage out of another 803' and it seemed fine.
I load tested the machine for about an hour, then shut it down. Next time I looked at it the gage was stuck down again.
Turns out that what is happening is that if you have 24V+ on the power wire and 24V- on the wire going to the mounting bracket stud and you suddenly loose all resistance to ground on the sensor lead ( open circuit ) the gage will peg itself hard to the left and the needle will get stuck against the side of the gage body.
If you remove the gage and whack it against the palm of your hand
, or something else... you can shake the needle loose and the gage should be fine.
In my case the sending unit inside the tank is dirty and seems to have multiple dead spots in it. It is currently soaking in cleaner and is about 90% functional now. Just 2 last dead spots that need more attention. Getting it out of the tank was a joy! Couldn't get it through the hole but found that removing the top half of the bracket and the top screw from the sensor body made it able to pull right out, no need to gut your arm wedged inside the tank!
If for some reason I can't get if to work 100% I know I saw a thread on here somewhere with a sender PN that is available on Amazon... if it comes to that.