Alpha 90020 Alternator Regulator is an internally regulated boat alternator controller that uses a switching mechanism on the negative supply to control the field current; it can be converted for external regulation by disconnecting its internal regulator and associated diode trio. Common failure points include degradation of the internal diode trio, shorted or open field winding connections, and drift in the voltage reference leading to over‑charging or under‑charging of batteries. First‑check diagnostics: verify the 12 V input supply and confirm proper polarity on the regulator terminals; inspect the diode trio for visual damage or burn marks; review any recorded error codes or irregular output voltage readings during a load test.[oss-gpt-20b]