Subaru Alternator Plug Replacement
What It Does: The alternator plug functions as a trigger to turn the alternator on (via the battery light on the dash) and senses battery charge to determine how much power to output.
Cars It Works On: All Subaru models built in 1999 or later including WRX, STI, EJ Engines built in 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, or 2018
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.