[77newell]

It sounds as if as soon as the solenoid kicks in to start the generator the voltage drops below that needed to keep the solenoid engaged, usually this is either bad batteries or resistance in the supply wiring between the batteries and the starter. If the drive engine starts just fine then the batteries and the connections at the battery are OK since starting the drive engine will consume a lot more power than our little ole generators. So I would suggest starting on the generator end cleaning terminals and the connections inside (I had an instance when the terminal to cable interface was corroded which I discovered by poking the voltmeter lead through the cable covering at the terminal and finding I had voltage in the cable but not on the terminal end when connected to the starter and engaged). The only way to test is with a voltmeter while the starter is attempting to engage, starting at the starter and working upstream. Ordinarily I would start at the battery end and work downstream but in this case we know that end of things is fine.

One other thing to bear in mind is that the ground from the generator to the chassis could be bad and cause the same symptoms (yup had that happen too, just not with my coach). The test for that is to test for voltage on the generator engine block to chassis ground while trying to start the gen.