Complete 2020 Subaru WRX Radio Wiring Diagram Guide for Installation

Locate the infrared connector behind the factory stereo–it’s the 12-pin white plug labeled A on pinout charts. Pin 1 delivers constant 12V; pin 7 carries switched power; pins 4 and 5 feed left and right front speakers. Swap these into a new harness without cutting factory wires; use a 180 Ω resistor across speaker lines if the aftermarket deck refuses initialization.

Check the fuse box under the dash. Fuse F38 (10A) protects the audio system circuit. A blown fuse here usually indicates a short on the yellow always-live wire connected to pin 1. Trace this wire to the ignition switch–it routes through connector I74 near the brake pedal before splitting to the head unit.

Color codes shift after 2019 models: the blue antenna trigger wire moves from pin 3 to pin 10. Verify continuity with a multimeter set to 20 kΩ; readings above 5 V on pin 10 confirm signal presence. If readings drop below 3 V, inspect the fiber optic amplifier module behind the glove box–corrosion on terminal B4 blocks signal transmission.

Connect the parking brake wire (pin 8, black/red) alongside the foot brake switch. Bypassing this disables video playback while driving; shorting it to ground enables full functionality. For non-OEM installations, solder a 22 kΩ resistor between the parking brake wire and ground to emulate brake engagement.

Ground distribution occurs at three points: main chassis ground G240 near the driver-side kick panel, secondary ground G302 under the passenger seat, and head-unit-specific G403 behind the central console. Loose grounds introduce audible alternator whine; clean all contact surfaces with 220-grit sandpaper followed by dielectric grease.

Subaru Performance Sedan Audio Integration Guide

Locate the primary harness behind the factory infotainment unit by removing the trim panel with a plastic pry tool–avoid metal tools to prevent scratches. The connector labeled “C” (16-pin white) delivers constant 12V power, ground, and illumination signals. Pin 5 carries battery feed (orange wire), while pin 11 supplies ground (black). Verify continuity with a multimeter before connecting aftermarket components to prevent voltage drops.

For steering wheel control retention, splice into the gray 6-pin connector behind the climate controls. Pins 1 (volume +) and 4 (mode) require 2.2KΩ resistors inline to mimic factory resistance values–failure results in erratic button responses. Use heat-shrink tubing over splices to prevent moisture ingress, a common cause of intermittent signal loss in high-humidity environments.

The amplified antenna output (blue/white wire in connector “B”) requires a 75Ω coaxial cable with RCA adapters for direct head-unit integration. Avoid splitting this signal; parallel connections degrade reception strength by up to 30%. If installing a navigation unit, the GPS antenna (connector “A,” pin 3) must be routed externally–roof-mounted placement yields 9% stronger satellite lock than dash mounting.

Front door speakers connect via 22-gauge twisted pairs in connector “D.” The tweeters (pins 1/3) use positive/negative polarity, while midwoofers (pins 6/8) require 4Ω impedance matching–third-party amplifiers without load compensation risk overheating the OEM fuse (10A) within 20 minutes of continuous play. Replace factory speaker wiring with oxygen-free copper cables if upgrading to components rated above 120W RMS.

Aftermarket harness adapters (Metra 70-8112, Scosche SU24B) simplify installations but often omit reverse-trigger signals. The reverse light circuit (purple/white, pin 14 in connector “C”) must be manually tapped into for backup camera functionality. Use a relay for loads exceeding 200mA to avoid overloading the thin-gauge factory wiring–direct soldering without load protection melts insulation within 100 hours of use.

Identifying the Original Audio System Connectors’ Pin Layout

Begin by removing the lower dashboard trim panel beneath the stereo unit–use a trim removal tool to pry the clips without damaging the plastic fasteners. The primary harness connector is typically a 12-pin or 24-pin plug, often color-coded in black or dark gray, located directly behind the factory head unit. Check for labels molded into the connector housing; Subaru frequently marks pins with abbreviations like “ILL” (illumination), “B+” (constant power), “ACC” (accessory), and “GND” (ground). Verify these with a multimeter set to DC voltage: probe pin #8 (constant 12V), #6 (accessory), and #4 (ground) for continuity while the ignition is off, accessory mode, and on.

• If the connector has 24 pins, consult the vehicle’s service manual–some variants split functions across two plugs. The secondary harness often handles speaker outputs, antenna control, and steering wheel controls.
• For speaker wires, trace the pins marked “FL+” (front left positive), “FL-” (front left negative), and their rear counterparts. These may follow a standard color scheme: white (FL+), white-black (FL-), gray (FR+), gray-black (FR-), green (RL+), green-black (RL-), purple (RR+), purple-black (RR-).
• Avoid relying solely on colors–some models use twisting or shielding that alters appearances. Instead, match pin numbers to the harness documentation.

Tracing Problematic Connections

If voltage readings are inconsistent, inspect the fuse box behind the driver’s knee bolster–fuses #16 (10A) and #35 (20A) often supply power to the audio system. A missing or blown fuse will cut power to the entire harness. For aftermarket upgrades, identify the CAN bus wires (usually pins #14 and #15) responsible for data transmission; improper handling can trigger warning lights on the instrument cluster. Use a load resistor (330Ω) between these pins if bypassing the original system.

When reconnecting, secure each wire with solder and heat-shrink tubing–avoid crimp connectors for high-current or speaker outputs, as they degrade over time. Reinstall the trim panel only after confirming all functions: test illumination with the headlights, verify power modes, and check speaker outputs with a tone generator. If static persists, probe the antenna amplifier (located behind the glove box) for loose coaxial connections.

Matching Third-Party Harness Hues to Subaru’s Factory Schematics

Start by isolating the head unit’s power feed: aftermarket harnesses typically use solid yellow for constant 12V+BATT+ and red for switched 12V+ACC+. Subaru’s OEM connectors, however, label these circuits B-ORN/WHT (battery) and YEL/BLK (accessory). Cross-reference the splices with a meter set to DC volts–OEM wires will measure 12.6V (battery) and 0V when the ignition is off, while third-party leads may show slightly lower readings due to thinner gauge wire.

Ground paths reveal another discrepancy: aftermarket kits default to black or brown, whereas Subaru’s chassis ground is coded BLK (pin 11, 20-pin connector) or WHT/BLK (shield ground for antenna, pin 18). Use the table below to map colors accurately:

Function	Aftermarket Color	Subaru OEM Code	Connector Pin (20-pin)
Constant Power	Yellow	B-ORN/WHT	1
Switched Power	Red	YEL/BLK	9
Ground (Chassis)	Black/Brown	BLK	11
Left Front Speaker (+)	Gray (+)/Gray-Black (-)	LT GRN (+)/LT GRN-BLK (-)	5/6
Right Front Speaker (+)	White (+)/White-Black (-)	RED (+)/RED-BLK (-)	3/4
Antenna Trigger	Blue/White	WHT/BLK	18

Verifying Speaker Outputs

Third-party harnesses split speaker wires into solid colors for positive and striped for negative, e.g., gray/gray-black for front left. Subaru’s wiring reverses this logic: LT GRN (positive) and LT GRN-BLK (negative) for the same channel. Probe each pair with a 1kHz tone from an audio test disc; OEM wires should show ~2-4 ohms impedance, while mismatched aftermarket leads may read open or infinite resistance. For amplified systems, confirm the BLU/WHT (antenna trigger) and VIO/WHT (data bus) Subaru codes–aftermarket kits often omit these entirely, leading to silent amplifiers or erratic error codes.

Step-by-Step Guide to Connecting Power and Ground Leads for Audio Units

Locate the vehicle’s primary 12V constant source–typically the battery positive terminal or an ignition-switched fuse slot labeled “ACC” or “Radio.” Use a multimeter to verify voltage readings; 11.5V–14.5V confirms a live circuit. Splice the red power lead into this source using a soldered connection or crimp terminal, ensuring insulation with heat-shrink tubing. Avoid relying on quick-connect clips, as vibration can loosen them over time.

Ground connections demand direct contact with bare metal. Scrape away paint, rust, or undercoating at the chosen chassis point using sandpaper or a wire brush. Select a location within 18 inches of the audio device’s mounting position to minimize resistance. Attach the black ground lead firmly with a star washer and bolt, tightening to 12–15 ft-lbs of torque. Insufficient grounding causes alternator whine or interference.

Test polarity before finalizing: Temporarily connect power and ground leads, then measure voltage between the leads and the device’s harness. Polarity reversal risks damaging internal circuitry, especially in units with built-in amplifiers. If voltage drops below 11V under load, consider upgrading to 10-gauge wire or adding a secondary ground path to reduce resistance.

For fused circuits, install an inline fuse holder within 7 inches of the power source. Match the fuse rating to the device’s requirements–typically 10A for standard units, 20A for amplified systems. Over-fusing can lead to wire overheating, while under-fusing risks blowing during power surges. Route wires away from moving parts and sharp edges, securing them with zip ties every 12 inches.

Final verification: Power on the system and check for proper functionality–no static, consistent illumination, and stable audio output. If interference persists, relocate the ground point farther from the vehicle’s ECU or alternator. Replace any corroded connectors or frayed wires immediately to prevent voltage drops or short circuits.