The small wire attached at the battery cable is the voltage source for the ammeter- - - -it supplies voltage to the ignition switch, headlights, and other circuits. The small terminal on the side of the 12V starter switch is connected downstream of the ballast resistor to supply full battery voltage to the coil during cranking. That wire was not used on 6V ignition systems, since there was no ballast resistor on a 6V coil.
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!