2003 Ford Focus | Stereo Wiring Diagram 2003 Ford Focus Stereo Wiring Information. Radio Constant 12V+ Wire: Orange/Black (Thick Wire) Radio Switched 12V+ Wire: Yellow/Green. Radio Ground Wire: Black/Yellow and Black/Green. Radio Illumination Wire: Orange/Black (Thin Wire) Radio Amp Trigger Wire: None. Left Front Speaker Wire (+): White/Black. Left Front Speaker Wire (-): Gray/Black. Car Stereo Radio Wiring Diagram - 2003 Ford Focus Car Stereo Radio Wiring Diagram – 2003 Ford Focus Whether your an expert installer or a novice enthusiast with a 2003 Ford Focus, an automotive wiring diagram can save yourself time and headaches. One of the most time consuming tasks with installing a car stereo, car radio, car speakers, car amplifier, car navigation or any mobile electronics is identifying the correct wires for a 2003 Ford Focus.