The illumination wire adjusts the brightness of the display on an aftermarket radio’s faceplate. This function is governed by whether or not the vehicle’s lights are turned on. This is not mandatory for proper stereo operation, so many installers leave it unhooked for maximum display brightness. However, if you want your particular radio’s readout to not be blindingly bright at night, make this connection with the other wires in your harness. Tips Warnings Writer Bio
