I assume you want to know about the surge suppressor provided in the rotating diode rectifier assembly of the alternator. If so, it is to protect the diodes from voltage surges.
can you tell that this surge suppressor is a kind of diode or not? Because i tried to test it using multimeter if it conducts only in one direction but i didn't find the diode charateristic in surge suppressor when tested using multimeter. Is that surge suppressor damaged??? Can you please tell me the ways to check the condition of surge suppressor of the rotating diode if it is working or not?