Good start! Now we can get down to the real idea of some things like how the generator gets power to start.
Have you had experience with hearing older cars just click, perhaps repeatedly as we tried to start them? That may be what you have going on with the generator!
You may be hearing a solenoid on the generator click but only once instead of the click, click, click, I mention.
So we can go to drawings and look at where that power comes from and what may be keeping it from getting there.
This should be the right drawing for a big part of what work the power on your RV.
Sheet 2 has a picture of the panel cover and label where they hide the parts. Got something like that, maybe on outside behind driver? No need to dig too deep to get to it yet, but good to know where this group is as it tends to be a big, busy part of our RV.
I did a snip from sheet 3 to mark some points to know about, if not now, for future understanding what often happens!
Click this drawing snip or go direct to the whole thing for better view?
This mode solenoid is what does two different things at different times when we want the coach and chassis batteries connected together.
The solenoid is just a switch that operates electrically when we put power on the small "control wires".
When we start the engine, there is a point they call ignition hot, which puts 12VDC on wire LR going down to the solenoid. That power goes through a coil in the solenoid and connects to ground wire FM which is often connected to the mounting screw for the solenoid. That gives ground both from wire FM and the mount, too.
The drawing makes it look like FM is on the big lug but it is actually on the ground mounting screw when we look!
So when we start the engine the solenoid connects left and right big lugs together and we have one big battery instead of two. As the engine runs and we drive home from camping, the engine alternator charges the coach AND the chassis batteries!
Second use is when we find we have a weak chassis battery and want to "jump start" it. We have a switch on /near the dash that is labeled different things at different times. AUX, boost, are a couple names that have been used, so some looking at what they called yours?
This is a switch which is momentary and connects power to wire LR again to connect the batteries together.
But this time, we are using the coach to help the chassis and before we were using the chassis to charge the coach!
Good system and does lots of good stuff but it also operates every time we start the engine and the contacts tend to arc and corrode more than we might like! Something to be aware of if the coach battery stops charging as we drive!
But the generator not turning wqhen we try to start it? Sounds like it is getting "some" power but not enought to turn over and crank.
When you are connected to shore power, there is a converter onboard which works to charge the coach battery and that is likely just enough higher voltage to let the generator go ahead and start at times but maybe not all the time?
I am guessing that there is a dirty cable somewhere along the path from the coach batteries to the starter solenoid on the generator itself???
See the red line come in from the coach batteries to the solenoid and a short cable to the coach battery disconnect relay? That relay has to operate and close to pass the power on through to much of the coach as well as the generator starter! Make sure the disconnect relay is operating when you push the disconnect switch. The switch may be near the door?
This is a special relay that latches in which position we last pushes the switch, on or off. See if you get lights inside when you push the disconnect switch. That will show the relay is actually moving and connecting power to the coach as well as toward the generator.
If power is getting through the disconnect relay, it is possible there is a dirty connection that keeps it from getting fully back to the generator.
If you open the generator cover, you may spot a big red battery cable coming in and you may need to test the 12VDC gets there???
Not at all unusual for some connection along the way to go bad when things set like RV do.
Back on the generator itself, there is likely to be a switch for starting the generator, instead of going insdie to a different switch. Maybe try that switch to see if it goes or if y9ou hear the solenoid there click? Normally somewhere near the near side and labeled. But there is also a breaker on the gen. so don't turn it off!
Nothing goes bad as quick as an RV that doesn't get used!!
I'll stop before I totally drive you insane!! Brain overload is a definite thing!!