OK finally fixed. I just decided to install a new ground wire from the battery negative to the frame. Drilled a hole, used some #10 wire to a self tapping screw. Tested, now have 12 when off shore power.
That opens up boondocking ahead. What a pain tracking down these electrical problems can be. Fortunately the Mobile repair guy I called yesterday never called back so that saved us several hundred bucks anyway.
I can use that 20 feet of #4 wire to hook up the inverter when I get the solar system fully installed.
Thanks for all the suggestions and help. I can only wonder what happened to the original ground wire that worked for 2 years+