The capacitor is used to protect the electronic equipment of the car and reduce radio interference.
Capacitor damaged or loose on alternator (poor ground contact) detected by an increase in radio interference when the engine is running.
Approximately the health of the capacitor can be checked with a megger or tester (on a scale of 1-10 MΩ). If there is no break in the capacitor, then at the moment the probes of the device are connected to the terminals of the capacitor, the arrow should deviate in the direction of decreasing resistance, and then gradually return back.
Capacitor capacitance, measured with a special device, should be 2.2 uF±20%.