Unless you're running an antique 3 brush generator without current and voltage regulation, a separate cutout relay isn't needed. A 3-unit regulator has a cutout built into it. It's the component under the cover behind the BAT wire connector. Lots of old tractors used 3 brush systems and a cutout relay. Ditto for 1930s cars and trucks.
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!