Directly replace the factory harness with a Metra 70-8114 adapter to maintain OEM functionality while upgrading the head unit. Verify pinouts against the Toyota Service Bulletin EL-0114–deviations risk erratic power delivery or amplifier shutdown.
For amplifier retention, splice the front/rear speaker outputs into the Scosche TA21 adapter, ensuring impedance matches at 4 ohms. Disable factory amplification via the brown/white wire (pin 17 on connector C) to prevent signal interference.
Color-code deviations exist between base and premium audio variants: light blue (steering wheel controls) differs from purple/black (auxiliary input). Cross-reference with a multi-meter before soldering connections–incorrect pairing triggers mute cycles.
Ground the black/yellow wire (pin 11) at chassis point G301 for stable voltage; improper grounding causes erratic display dimming. For rear-view camera integration, route the pink/black wire through the original loom, avoiding tension on the harness.
Disable the speed-sensitive volume via CAN bus pin 12 (green/red); failure to do so distorts audio at highway speeds. Use a PAC RP4-CH11 interface for seamless steering wheel control retention–aftermarket units often misinterpret the original protocol.
Guide to Installing an Aftermarket Sound System in Your GT86
Start by disconnecting the negative terminal on the vehicle’s battery to prevent electrical shorts. Locate the factory harness behind the dashboard’s center panel–this connects to the OEM head unit via a 20-pin Metra connector (part #70-8114). Match each wire to the color codes below to ensure proper integration with aftermarket systems. Failure to verify connections risks damaging the vehicle’s electrical modules.
The following table outlines the standard wiring configuration for the base model’s audio interface:
| Function | Wire Color (Factory) | Aftermarket Connection |
|---|---|---|
| Constant 12V | Yellow | Red (or yellow on most decks) |
| Switched 12V | Red | Yellow (or red) |
| Ground | Black | Black |
| Front Left (+) | White/Light Blue | White |
| Front Right (+) | Gray/Red | Gray |
| Rear Left (+) | Green/Black | Green |
| Rear Right (+) | Violet/Blue | Purple |
| Antenna Trigger | Blue | Blue |
| Illumination | Light Green/Red | Orange/White |
Use a multimeter to confirm voltage on the yellow wire (12V constant) and red wire (12V switched) before splicing. The black ground wire should register 0 ohms against the chassis. Avoid using the factory ground point behind the glove box–opt for a dedicated bolt near the transmission tunnel for more stable grounding.
Integrating Amplifiers or Signal Processors
If adding an external amplifier, tap the front and rear speaker wires before they enter the OEM harness. For clean signal transmission, use a line output converter (LOC) on the factory speaker wires rather than interfacing directly with the head unit’s RCA jacks. The LOC prevents feedback and preserves factory settings like warning chimes.
For vehicles equipped with steering wheel controls, retain functionality by installing a PAC RP4-GM54 adapter. Connect the adapter’s input wires to the clock spring’s harness behind the steering column–specifically the pink, black, and white/green wires. Failure to properly integrate these connections will disable cruise control and audio controls.
Secure all splices with solder and heat-shrink tubing; electrical tape degrades over time. Route new wiring away from sharp edges and moving components (e.g., pedals, seat tracks). Reconnect the battery last and test all functions before finalizing the dashboard assembly.
Identifying Aftermarket Audio System Connector Terminals for the Toyota 86 Variant
Locate the 16-pin harness adapter beneath the dashboard’s lower trim panel on the driver’s side–remove the single Phillips-head screw securing the panel to access it. Pin assignments for the aftermarket unit follow this layout: terminal 1 (constant 12V+), terminal 4 (illumination), terminal 7 (left rear speaker+), terminal 8 (right rear speaker+), terminal 10 (antenna trigger), terminal 12 (ground), and terminal 13 (power antenna/output). Verify continuity with a multimeter against the vehicle’s original-equipment connector to confirm polarity before soldering or crimping.
Connect RCAs to the pre-amp outputs–front channels map to pins 1 and 2, rear to pins 3 and 4–using shielded cables to minimize interference from the adjacent CAN bus wires (pins 5, 6, 9, and 16). Install a fusion bypass module between the OEM harness and aftermarket head unit to prevent amplifier shutdown errors; the module’s red wire splices into terminal 1, while the yellow wire taps terminal 10.
Step-by-Step Guide to Identifying Stock Head Unit Connector Colors and Functions
Locate the factory harness behind the dashboard mounted unit. The primary plug typically has 16 to 24 pins arranged in two rows. Use a multimeter set to continuity mode to verify pin assignments without relying solely on color coding, as variations exist between trims and model years.
Identify the constant power wire, usually red or yellow, delivering 12V regardless of ignition state. Verify by testing voltage with the key off–if voltage drops below 12V, it’s not the correct lead. The switched power wire, often blue, gray, or violet, activates only when the ignition is turned to ACC or ON.
Ground connections are almost always black or brown. Probe these with the multimeter’s black lead on the vehicle chassis and the red lead on the wire–zero resistance confirms a proper ground. Avoid assuming green or bare copper wires are grounds unless tested, as some systems repurpose these for low-level signals.
Speaker outputs can be trickier. Front left positive is typically white, front right positive gray, rear left positive green, and rear right positive purple. Stripes or tracers–usually black–indicate the negative speaker leads. Use a 9V battery to briefly tap each speaker wire; a faint pop confirms the connection without damaging the system.
Data communication wires, like the CAN bus, appear as solid orange or light green with a stripe. These require specialized tools like an oscilloscope for proper analysis, as probing them with a multimeter can corrupt onboard modules. Look for bundled wires entering a single connector–these often carry serial data.
Illumination and dimmer wires control display brightness. These are orange or light blue, adjusting voltage when the headlights are on. Test by turning the headlights on and measuring voltage changes–expect 0-12V swing as you rotate the dashboard dimmer switch.
For auxiliary inputs or steering wheel controls, trace the thin wires bundled separately from the main harness. These are often clustered in a smaller 6-8 pin connector. Switched signals here operate at lower voltages (5V reference), so set the multimeter to the 20V DC scale to avoid misleading readings.
Common Install Mistakes When Splicing Into Factory Harnesses on Coupe Variants
Avoid taping splices with electrical tape alone–it degrades under heat and vibration, leading to intermittent connections. Use adhesive-lined heat shrink tubing rated for automotive use (minimum 4:1 shrink ratio) and a butane lighter or heat gun to ensure a sealed bond. Test continuity with a multimeter before securing the splice; even a 0.5-ohm resistance can cause audio distortion or voltage drop in aftermarket head units.
- Stripping more than 6mm of insulation exposes copper strands to moisture, accelerating corrosion. Use precision wire strippers (18-22 AWG setting) instead of teeth or scissors.
- Twisting strands counterclockwise before soldering loosens connections over time. Rotate clockwise, apply rosin-core solder at 350°C, then crimp a non-insulated butt connector for strain relief.
- Ignoring factory fuse ratings risks blowing the accessory circuit. Match aftermarket amplifier fuses to the OEM fuse value (typically 10-15A) and route power cables away from ABS sensors.
- Skipping ground verification invites engine noise. Scrape paint off chassis ground points and torque to 8-10 Nm; a poor ground under 0.2 ohms causes silent failures weeks post-install.
Testing Speaker Outputs Before Finalizing Head Unit Installation
Use a 1 kHz sine wave test tone at -12 dB to verify speaker polarity immediately after connecting harness adapters. Connect multimeter probes to the positive (typically yellow/white) and negative (solid color, often black or brown) wires–reverse polarity registers negative voltage. If readings swing positive, swap wires at the harness.
Playback testing demands a structured approach:
- Left front: Isolate by muting other channels; run pink noise through a 4Ω resistive load before speaker attachment to confirm head unit DAC integrity.
- Subwoofer: Send 40 Hz tone–if cone movement isn’t visibly outward, check amplifier remote turn-on (blue/white) and ground (bare) for 12V potential.
- Tweeters: Sweep 3 kHz to 8 kHz–faint distortion or rattling suggests faulty crossover or improper mounting.
Connect an audio signal generator to the RCA preamp outputs (if available) with a Y-splitter. Feed 0.5V RMS at 1 kHz into both channels–balance discrepancies exceeding 0.2V RMS indicate faulty output transistors or corrupted DSP settings in premium models. For OEM replacements lacking RCA outputs, tap into the speaker wires directly with alligator clips, ensuring signal generator ground matches chassis ground.
Troubleshooting Signal Loss
If no sound is detected:
- Verify fuse continuity in the accessories circuit (typically 10A or 15A).
- Test harness adapter pins for bent contacts–use needle probes to measure voltage at each speaker terminal with ignition on (should read 6-8V DC offset).
- Check for parasitic loads: disconnect non-essential modules (amplifiers, lighting) during testing.
- Inspect for stray strands at crimp connections–solder and heat-shrink any frayed copper.
Dynamic testing requires a 5-minute warm-up cycle for solid-state components. Run a full-range frequency sweep (20 Hz–20 kHz) at moderate volume–clipping above 80% suggests insufficient power supply regulation or undersized speaker impedance (replace 2Ω-rated components if pairing with 6×9 drivers). Log voltage drop readings across the battery terminals at idle (zero drop) and during sweep testing (maximum 0.4V drop tolerable).
Finalize by securing all connections with nylon wire ties and dielectric grease. Re-test after 24 hours–environmental humidity may expose latent solder joint oxidation or improperly torqued ground mounts (target 8–12 Nm with a torque wrench).