With the eng on a fast idle and all lights/accessories OFF then take off the green wire from the alt field terminal & jump 12V from the batt positive terminal to the male terminal on the alt that you just removed the green wire connector from & see if it charges. Keep the jumper on there for 3 seconds max just long enough for you to look at the meter & get a reading & likely you'll hear the eng slow down slightly as the alt engageing from this "full fielding" will drag the eng speed down slightly but enough to notice. this'll tell you the alt is good/brushes have continuity