Pump should run when you hold the Start/Stop switch to OFF. If you disconnected from the Carb, it should pump gas into a can.
When it quit, acting like it was out of gas, the On/Off Switch should have winked out a Trouble Code. I want to say "36" which would show as "--- ------" is a non-specific "Dunno what Happened" code commonly associated with Out of Gas.
As CD said, if you've got it connected to a battery or charger, polarity's right, it should pump.
In a green ONAN box, that part is around $100. There are un-branded replacements on Amazon for around half that. My guess is they're made by the same bunch on the same bench in China.
You CAN substitute a low-pressure auto supply pump (3-5-psi) but ONAN would say they aren't legit unless they serve as fuel shut-off when not running. You "should" have a dedicated genset fuel pickup on your main chassis tank. I don't think your non-running genny would siphon your main tank through its pump, filter and carburetor. The Needle/Seat valve would have to leak also. So that could be your quick fix if your proper part doesn't come through. MrGasket, Purolator, NAPA, etc. Just get Low Pressure.
2014 sounds like the part might be under warranty. Getting to the right place in time to actually exercise it probably suggests fixing it yourself.
From all you say, unless the pump isn't getting power from the control board or isn't grounded, it's bad. If you applied battery to the hot terminal and grounded the pump, it's bad.
Still, if a crack or pinhole developed in the lines or the strainer on the suction side of the pump and it's sucking air, will probably run out of gas...
