Check the brooms of the regulator in case they did not make good contact due to wear or dirt of the collector, also check the alternator cable to battery (including the interior of the terminal) that sometimes sulfate and make not good contact. In general, the alternator is usually quite hard and the problem is usually broom or excited cable (cut cable or poor contact) that does not induce and then the alternator does not work; That's why I don't tell you to check the diodes bridge or anything like that ... greetings !!