In short, the illumination wire on a car stereo wiring harness is used to dim the screen on your aftermarket car stereo. The wire is connected directly to your instrument cluster and provides a negative trigger or positive trigger that tells your radio when you turn on and off your headlights.
Not having a bright car stereo screen shinning in the corner of your eye while you drive down a dark interstate highway could prove to be a life saver.
How to use the illumination wire on a car stereo
Using the illumination circuit in a vehicle is fairly simple. The first thing to do is to verify that you actually have a connection for that option on your factory radio harness (the harness you unplug from your factory radio).
To do that, a little trick we do is to clip on your aftermarket harness to your factory harness. After its snapped on find the orange wire with the white strip.
Follow that wire to the factory harness and see if there is wire in that same pin location. If there is, this is a good indication that your aftermarket radio can take advantage of a factory dimming option.
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How to Connect an illumination Wire on an Aftermarket Radio
After you’ve verified that your vehicle has an illumination wire on the factory harness, its time to connect these wires.
This process is done along with the wiring of your aftermarket stereo. Connect the orange wire on the new radio harness to the orange wire with the white stripe on the aftermarket harness that clips onto your factory harness.