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.
Disconnect the negative battery terminal under the hood, using the socket wrench and the correct insert.
Locate the orange wire leading from the back of the stereo's wire harness. On some models, this is also sometimes a reddish-brown color. Consult the manual or the label affixed to the top of the radio to confirm the wire coding for you particular model.
Find the matching wire on the wire harness adapter, used to interface with the factory harness in the dash cavity. Note that the aftermarket adapter's color scheme will match the vehicle's wire colors, not necessarily the stereo's. Look closely at the labeling on the wire harness adapter to ascertain which wire is the illumination lead.
Strip 1 inch from the flying end of both illumination wires. Insert the wires into opposite ends of a 16-gauge crimp connector.
Align the crimp connector above the connector's collar into the jaws of the crimp tool. Squeeze firmly to secure the wires into the connector.
Match, strip and connect the remainder of the harness wires as needed in the same manner.
Reconnect the negative battery terminal after all harness wiring is complete. Turn on the radio and test by turning the headlights on. The radio should dim with the lights on, then return to normal brightness when off.
- Dayrunner headlights should not cause the stereo to dim. However, automatic headlamps will if the vehicle's sensor detects low ambient light.
- Never make car stereo connections with the system or vehicle turned on.
- Socket wrench and insert
- Aftermarket wire harness adapter
- Wire strippers
- 16-gauge insulated crimp connector
- Crimp tool
- Thomas Northcut/Photodisc/Getty Images