Howdy,
First, do you know how the aux fuel works?
The MEP generator has a internal fuel tank. Sometimes called a day tank. When the S-1 is set to make use of the aux fuel, the day tank is used. When the day tank gets low (adjustment can be made here) it turns on the aux fuel pump. (Aux Fuel connection by the fill cap) That fuel is added to the day tank. It automatically shuts off when it gets around 80% full (This can be adjusted) The sequence of auto filling will continue until there is no fuel left in the aux tank. The generator will keep operating until that day tank is just about empty, and at that time, you will get a "Fault" Low Fuel, and the generator will shut down.
NOTE: Do NOT trust the aux fuel refill to work.
Test it out. You can manually reach in the fuel tank and moves the floats to simulate a low fuel condition. The same thing for the float level to signal aux fuel pump to stop.
We had members which ended up with multi-gallons of diesel on the floor.
Another testing method, would to have it all connected and running, use a siphon hose to empty the day tank, watch and listen to when the aux pump kicks on. Note the fuel gauge level. Watch and listen to when the aux fuel shuts off. 70-85%. This can be adjusted overall with the exact height of the dual float fuel level sensor. The important part is that it actually shuts off the aux fuel pump. If not, you could have 275 gallons on the floor.