What's it do? This simple module plugs in to the back of the stock tail light housings on the 2015+ Subaru WRX and WRX STi and moves the separate turn signal (a 7443 bulb) to the stock brake light position. This allows the 7443 socket to be freed up, which can then be upgraded alongside the 921 reverse light for additional back up lighting intensity! Installation Process No tail light removal necessary! These in-line harnesses do all the work for you. Just match up the stock connectors on each side and plug 'er up! About that T-Tap The remaining connector (a blade terminal / t-tap) allows you to select if and how you want the OEM turn signal socket to receive power. For this, you must use an LED bulb as incandescent bulbs (like stock) require too much power. Green = Backup Light. Red = Turn Signal. Yellow = Running Light. Black (Input Side) = Brake Light. Black (Output Side) = Brake and Turn Signal.