What was found
(CAN) THE NR 2 GENERATOR CAUTION LIGHT ILLUMINATED ON THE CAWS PANEL. THE PILOT NOTED THAT THE NR 2 GENERATOR OUTPUT WAS FLUCTUATING BETWEEN A 60AMP DISCHARGE AND A 20 AMP POSITIVE CHARGE. HE TURNED THE GENERATOR OFF, THEN RE-SELECTED IT TO THE ON POSITION.THE RESET WAS SCESSFUL FOR APPROX. 20 MINUTES AT WHICH TIME FOR APPROX 20 MINUTES, THE PROBLEM REOCCURRED. MAINTENANCE FOUND THAT THE BRUSHES WERE WORN WELL BEYOND A SERVICEABLE LIMIT. A NEW SET OF BRUSHES WAS INSTALED AND THE AIRCRAFT GROUND RUN. NO FURTHER PROBLEMS NOTED.