we  had a  very similar problem with our  new 210 AC

I even  used my   volt meter to &quot;PROVE&quot;  it wasn't  a ground problem -- it just had to be  the  starter....    ( the starter even had its own ground wire to the block) 

dad said   HUMOR ME one more time and  run  another ground to the  base bolt of the starter...

instead of  the  4 big 12v's   ( 950 CCA)    we  have  1 550cca napa car battery  starting it  now.....