Complete 2009 Subaru Legacy Radio Wiring Diagram and Color Code Guide
Locate the factory stereo harness behind the dashboard’s lower panel on the driver’s side–disconnect the battery first. The primary power lead, yellow (constant) and red (switched), must match the aftermarket unit’s ignition wire to prevent drainage. Verify ground connections (black or brown) with a multimeter; resistance should read under 0.5 ohms for stable performance.
Speaker wires follow a standard color code: white/white-black (front left), gray/gray-black (front right), green/green-black (rear left), violet/violet-black (rear right). Cross-check with an audio test tone before finalizing connections. Illumination control (orange or orange-white) adjusts display brightness–connect to the vehicle’s dimmer circuit if compatibility is required.
For steering wheel controls, use an adapter (Metra ASWC-1 or PAC RP4-CH11)–program it according to the stereo manufacturer’s instructions. Install an inline fuse (10A) on the yellow power wire near the battery. Reconnect the battery, then test all functions (volume, balance, fader, seek) before reassembling panels.
Electrical Connection Guide for Factory Audio System in Mid-2000s Sedan Models
Locate the harness behind the dash panel on the driver’s side to begin installation or troubleshooting. The main connector (16-pin, typically white or gray) splits into power, speaker, and antenna outputs. Pin 1 (red wire) delivers constant 12V from the fuse box–verify voltage with a multimeter before connecting aftermarket units. Pin 2 (yellow) carries switched power from the ignition circuit; a faulty relay here may cause intermittent shutdowns. Ground (black or brown, Pin 6) must attach directly to chassis metal–scratch paint if corrosion is visible.
The speaker wires follow a consistent color-code: front left (+) is light green, front right (+) light blue, rear left (+) dark green, and rear right (+) dark blue. Negative leads (-) share matching solid colors with added black stripes. Aftermarket adapters often mismap flat harnesses–use a T-harness splicer (Metra 70-1761 or equivalent) to avoid damaging factory plugs. Test each pair with a 1.5V AAA battery before finalizing connections; a faint pop confirms polarity without risking amplifier damage.
Critical missteps to avoid: Never tap power wires from the cigarette lighter circuit–it lacks sufficient amperage for modern head units, leading to erratic behavior. The antenna trigger (Pin 10, blue) only engages when the original tuner is present; bypass it for non-OEM setups using a 12V relay or resistor. If retaining steering wheel controls, procure an interface module (Axxess ASWC-1 or iDatalink Maestro RR) rather than splicing directly into the CAN bus wires (gray and white, Pins 12-13).
Harness Pinout Reference for Quick Diagnosis
Below is a breakdown of the 16-pin connector’s function by position (viewed from the wire side):
- Pin 1: Battery (+) / Red
- Pin 2: Ignition (+) / Yellow
- Pin 4: Illumination / Orange (dims with headlights)
- Pin 5: Power Antenna Trigger / Blue
- Pin 6: Chassis Ground / Black
- Pin 8: Front Left (+) / Light Green
- Pin 9: Front Left (-) / Light Green/Black
- Pin 11: Front Right (+) / Light Blue
- Pin 12: Front Right (-) / Light Blue/Black
- Pin 14: Rear Left (+) / Dark Green
- Pin 15: Rear Left (-) / Dark Green/Black
- Pin 16: Rear Right (+) / Dark Blue
- Pin 13: Rear Right (-) / Dark Blue/Black (or unused in some models)
Measure resistance between Pin 6 and suspected ground points–values above 0.5 ohms indicate a poor connection demanding attention. For vehicles equipped with navigation or premium audio, an additional 22-pin connector (purple) handles data and amplified outputs; leave these untouched unless replacing the entire infotainment stack.
When replacing the head unit, secure all loose wires with braided loom and zip ties routed away from pedals or HVAC ducts. Loose cables near the fuse box can short against terminal blocks, triggering diagnostic codes (B1801 for audio system faults). Label each wire with masking tape during disassembly to eliminate guesswork during reassembly. For persistent no-power issues, trace the red wire upstream to the fuse block (Fuse #19, 10A) and inspect for melted contacts–a common failure point aftermarket installations.
Finding the Original Audio System Plug in Your Vehicle
Begin by removing the lower dashboard trim panel on the driver’s side. This panel is secured with two clips near the fuse box and one screw beneath the steering column cover. Use a plastic prying tool to carefully release the clips without damaging the plastic tabs.
The factory harness connector sits behind the climate control unit, slightly offset toward the center console. It’s a rectangular plug with 16 to 20 pins, depending on the trim level, and typically gray or black in color. Look for a bundled set of wires exiting the main wiring loom–this identifies the audio interface.
If the connector isn’t immediately visible, trace the wiring from the back of the audio head unit downward. The wires run vertically behind the hazard light button and intersect with the main harness near the transmission tunnel. Gently pull aside any cable ties securing the bundle to expose the plug.
- Unplug the hazard switch temporarily if it obstructs access.
- Check for a secondary small plug (usually 4-pin) connected nearby–this may be the amplifier interface on premium models.
- Avoid tugging on wires; instead, wiggle the connector gently to release it from its mounting bracket.
On base models without an amp, the connector may be directly attached to the head unit harness. In premium versions, the plug includes thicker gauge wires for amplified signals–these often have orange or purple stripes for RCA-level audio output.
Identifying Pin Layout Without Documentation
Use a multimeter set to continuity mode to match pins to functions:
- Locate the constant 12V wire–it should register battery voltage even when the ignition is off.
- Find the accessory voltage wire–this activates only when the key is turned to ACC or ON.
- Ground pins will show 0 ohms when probed against the chassis.
- Speaker wires alternate between positive and negative–test by briefly touching them to a AA battery (positive wires will cause a faint pop).
Mark each identified wire with masking tape before disconnecting anything. The factory harness typically includes colored wires: solid colors for speaker outputs, striped wires for signal returns, and single-color thick wires for power feeds.
For aftermarket installations, note that the OEM plug may lack RCA-level preouts. If adding an amplifier, the rear speaker wires (usually gray and green) often serve as high-level inputs–tap these carefully to avoid signal loss or interference.
Matching Power and Ground Conductors: Color Codes and Terminal Positions
Start by locating the solid yellow cable–this is the primary constant-voltage feed, typically rated for 10A. Trace it back to the 16-pin harness connector at the rear of the head unit, specifically terminal 4. Verify continuity with a multimeter set to DC voltage; readings should hold steady at 12-14V regardless of ignition state. If voltage drops below 11.5V, inspect the fuse link (usually a 15A blade fuse inline near the junction box) for corrosion or oxidation.
For switched power, identify the red wire with a thin white stripe–this conductor energizes only when the ignition is in the ACC or ON positions. Its pinout sits at position 7 in the same 16-way connector. Cross-check by cycling the key; voltage should spike to 12V during ACC/ON and drop to 0V in OFF. A failed reading often indicates a blown accessory fuse (commonly 10A) or a break in the harness near the steering column.
Ground connections rely on three distinct paths:
- Black wire (terminal 5) – Main chassis return, secured to a factory-ground stud behind the dash cluster. Ensure bare metal contact; paint or rust here causes intermittent audio dropouts.
- Brown wire (terminal 10) – Dedicated signal reference for amplifier circuits. Verify direct continuity to the vehicle’s central grounding plate.
- Dark green/black tracer (terminal 8) – Shared return for illumination controls, often overlooked. Test with a low-resistance ohmmeter; readings above 0.5Ω suggest a faulty crimp joint.
When reconnecting terminals, avoid mixing switched and constant feeds. Misrouted power risks draining the battery in under 12 hours or frying the internal voltage regulator. Label each cable with masking tape immediately after disconnecting–manufacturer color deviations exist, especially in premium trims where orange replaces red for illumination leads. Consult an aftermarket adapter harness if colors diverge from standard ISO norms, as forced pin swapping can void onboard diagnostics compatibility.
For troubleshooting persistent hum or radio interference, focus on the ground side first. Use a jumper wire to bypass the factory harness, connecting the main ground (black) directly to a known clean chassis point like the gearbox mounting bolt. If noise diminishes, the issue lies in a corroded ring terminal or insufficient torque on the existing ground screw. Never rely on solder alone for ground repairs–crimp the connection with a heat-shrink butt splice for mechanical stability.
Critical Pinouts to Memorize
- Terminal 4 – Yellow: B+ constant (fused 15A)
- Terminal 7 – Red/white stripe: Switched ACC/ON (fused 10A)
- Terminal 12 – Pink: Illumination dimmer (links to headlight switch)
- Terminal 6 – White/blue stripe: Antenna motor trigger (12V momentary pulse during power-up)