squareback alternator wiring in pre 70 car issue

do NOT drive it with it charging that high as that will fry bulbs/electrical devices that are "on" (they ain't made to handle 15+ volts). You have the blue wire to the OE type "box" reg then the green wire from the reg "fld" terminal out to the alt, to one of the alt field terminals and the other alt male field terminal is grounded to the alt case? Most common is a bad reg. the alt innards are OK cuz you had it tested & assuming the green wire ain't grounded. also the battery must be fully charged & able to take/hold a charge (not sulphated or other battery specific ills).