Electrical problem in 03 Southwind 32V

With the coach engine running you are getting 12VDC from the engine alternator. With the generator running or on shore power you getting power from the convertor. A possible problem is the battery disconnect solenoid contacts are bad. But before you start spending money do a good cleaning of the battery posts and terminals. Then check the grounds between the battery and the coach frame. If all the tie points look good then dive into the battery control center ensuring all the tie points there are clean and tight. If that doesn't fix the problem then I think the solenoid has failed. Easy fix and costs around $20.

But first do as Dog Trainer suggested and check the batteries at the posts not the terminals. Yes it makes a difference. One dirty terminal of the battery pair will cause problems.