It's possible that the cutout relay setting is too high- - - -failing to complete the circuit between the generator and the battery unless the field is grounded. That's a simple check for anyone familiar with servicing and setting DC regulators, but it's nearly impossible to explain with a keyboard. PM me for a phone number and I'll try to talk you through the regulator diagnostic and setting steps. It's not uncommon for even brand new regulators to need adjusting to work right. I've got a mid-1950s version of the manual you referenced- - - -very good information!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!