That terminal marked "G" in the left diagram certainly looks like a ground, unless electrical symbols have changed recently. The right figure completes the point closing magnetic coil circuit by going back to the generator.
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!