What the hell?
That Onan has a CENTER TAPPED 240VOLT STATOR!
EACH 120 volt receptacle uses an OUT OF PHASE HOT. L1 and L2. L0 NEUTRAL is the third slot in that 240vac receptacle. Generators from 100 watts to 100 megawatts DO NOT USE A GROUND. GROUND IS EARTH. TERRA FIRMA. Where do you think that third terminal connectuon goes? Mars? It goes directly to the center tap of the stator.
PROVE IT WITH A VOLT METER
The voltmeter proofing should have been the first and only answer many of you should have given.
E=MC2 assumptions always make me grumpy. OK sue me - grumpier.
Here's a guy who needs a generator and was getting his arm twisted that it could't work.
It helps to have had something apart and physically see how it works then check it with instruments. It and a few several dozen like it.
STRUCTURES may have 3-prong connectors for stoves and dryers that have two phases and an earth ground. But generators have neutral in receptacle connections. EARTH GROUND CONNECTORS are usually an aluminum block bolted to the machine's frame that has a hole and set screw. A wire is attached from there to a stake driven into the ground.