The last post is true.
Some comments: The following observations are made on my coach, yours, of course may be wired differently Except for the first one
Question above: Dosen't shore power charge house batteries?
Observation: When Engine running, RV is often Rolling, Rolling, Rolling down the highway.. Thus shore power is... NOT.
Comment: if Salesman switch was off nothing 12 volt would work.
Observation: when my coach engine is running OR I have shore/generator 12 volt works no matter the position of the salesman switch. Since all charge points are on the HOUSE side of the world.
Best advice: If the solenoid has been replaced, with the proper solenoid, and it is NOT warming up as you drive.. Something wrong with control, likey a blown fuse.
Observation 2: You likely have the incorrect solenoid.. As I said, they look a lot like (identical in many cases) to a Ford Starter Solonoid.
But internally there are MAJOR differences.
Home is where I park it!