RV Repair: Onan 4.0 Gas Generator, itasca suncruiser, gas generator

Question
I have a '96 Itasca Suncruiser 29RQ (just purchased) equipped with an Onan 4.0 gas generator.  The genset runs and starts fine as long as the coach engine is also running.  Will not start if the coach engine is not running.  Is this a battery problem?  Genset breaker and fuse are OK and fuses in converter are OK.  No dim lights when using auxilary battery.

Answer
It sounds as if the gen is not getting a good connection with the battery, you may be wired before the battery but after the alternator and that would explain it starting when the engine is running, If you follow the lines with your meter you may find a loose or corroded connection to the battery. It would show 12 volts but wouldnt pull the amps needed to start. You can check that by putting the leads of your meter between the gen and the 12+ volt feed and try to start it. If the voltage just goes away then it will be a connection or an inline breaker.