Here is a troubleshooting guide. The next step should be checking the low oil pressure switch to make sure it is functioning.
Q
. Why does my generator start and then shut down as soon as the start switch is released?
A
. Most models require both oil pressure and AC voltage from the generator to keep running. A lack of AC voltage can be caused by a variety of problems involving the control board, regulator, generator and wiring. A stuck oil pressure switch can also cause this symptom. The interaction between the various components of the system can be confusing during troubleshooting. Use the Troubleshooting Guide to isolate the problem
Guide is at http://www.flightsystems.com/pdf/onan-rv-troubleshooing-guide.pdf
