This is a plug and play signal harness for adding a connection to the WRX or STi. These cars never came with the conection to power the signal light in the bumper. The harness T's between the main body harness of the car and the signal bulb. Creating a clean and simple install and eliminates the requirement to splice into your factory harness. It's main purpose is to power the JDM fog bezels but it can also be used to power other light sources such as C-lights or halos.