My well pump was replaced recently, so I do a complete teardown and diagnosis on the old pump, including going through how it works. There is one mystery component that I'm not sure about. Is it a temperature sensor? It might be a lightning arrester. Do you know? Leave a comment.
ANSWER: It's a 'biac start switch' which supplies power to the start winding while the motor is starting up, then power is cut when it gets to rated speed. http://apps.franklin-electric.com/am/biac-switch/standard/index.html