Three possible answers .. Note this assumes the generator actually runs.
Some background: If the generator fails then in the case of most modern ONAN generators the generator will shut off soon as you release the START button and give you a low-battery, not cranking fast enough, code. You know it was cranking fast enough cause you heard it start.. ONAN monitors the output and shuts down if it is not within lmites.
now: The suspect list:
#1 and 2 are circuit breakers on the Generator itself.. On mine unless the sun is at just the right angle it is hard to read the OFF and ON labels (There is no "tripped" position) so I stuck a peal and stick on to indicate, in my casem, the OFF position (since that side had room for it) Brother P-Touch, always at your side.
Suspect #3 is the transfer switch.. IF YOU HAVE ONE,, sometimes they fail to transfer.. This is epically true if you start the generator while connected to shore power (or shut down while connected to shore power) and have Air Conditioners running. this can cause one heck of what is called an "inductive spike" which arcs across the contacts and welds them in position.
Suspect 4 is also the transfer system.. On some RV's it is manual, You need to plug the shore cord into a matching outlet on the RV.
