Help with a Class A Tradewinds

[Halfdane]

I'm working on an old 2006 Tradewinds Class A motorcoach. I was called out to do repairs to the coach and, in addition, get all the coach batteries and chassis batteries replaced. The owner stated that the generator and coach wouldn't start. After replacing all the batteries, the generator started fine, but the coach was behaving in the following way. Any ideas on where to look for a solution? Thanks.

 

[Aa1ssradio]

Looks to me like there is not enough voltage on the chassis side. Maybe a bad ground??

 

[Halfdane]

Is there a common point that a bad ground can be found? It could cost the owner a lot of money for me to hunt down a bad ground in a large motor coach.