How to Know if you Have an Issue: You can tell your alternator plug needs replacing if there are cracked tabs or rusty terminals. You want an intact plug and clean terminals to ensure the plug stays locked and has a good connection.
2 Wire vs. 3 Wire Alternator Plugs: Some models have 2 wires in the alternator plug and others have 3 wires. It varies from model to model so the best way to tell what you have is to look at your alternator plug. You can visually check if the plug has 3 wires or 2 wires with a cavity plug. Please note that if you have an alternator plug with 2 wires, it must have a cavity plug! Otherwise, you will lose the waterproof seal in the plug and have a lot of issues down the line. In case you're wondering, the third wire in the 3 wire alternator plug is a connection to the ECU so the ECU can adjust the alternator output voltage depending on need.
Alternator Plug A can be found on all EJ platforms from 1999-2022 which would include all STi models, WRX models 2002-2014, Forester Models 1999-2013, Legacy Models 1999-2012, Impreza Models 1999-2011
Alternator Plug B fits Impreza models from 1993-1998, Legacy Models from 1995-1998, and the 1998 Forester.
Alternator Plug C is Found on many FA/FB powered Models
