These contact points get power to the electromagnet. When the electromagnet is energized, it moves the spring steel diaphragm, which also opens the contact points. The electromagnet is then de-energized, relaxing the diaphragm when the contact points open, which also closes the points. This happens hundreds of times a second to create a buzzing action and rapid movement of the diaphragm. The nut adjusts point gap, which narrows the window of operation. When the contact points get dirty or corroded, horn operation becomes erratic or silent.