Alpine 4 Channel Amplifier and Powered Subwoofer Installation Guide | 2010-2024 4Runner

🛠️ Please read this entire guide before beginning your installation:

Your kit now includes the updated Alpine KTA-450 amplifier, which is different from the amplifier shown in the installation video below.

The installation video can still be used as a general guide. However, some amplifier connections, settings, and installation steps have changed with the KTA-450.

Please follow the written instructions in this guide whenever they differ from the video.

If you have any questions during your installation, please contact our support team at support@trailgridpro.com.

Welcome to the installation guide for your 2010-2024 4Runner Alpine Plug & Play 4-Channel Amp & Powered Subwoofer Kit from Trail Grid Pro! This step-by-step guide is designed to make the installation process as smooth as possible, whether you're a seasoned DIYer or tackling your first head unit upgrade.

In this guide, you’ll find:

• 📢 Important Updates: The written guide includes the latest updates and adjustments that may not be shown in the video, ensuring you have the most up-to-date instructions for a flawless installation.
• 🎥 Installation Videos: Visual instructions to help you through the process, including a detailed microphone install.
• 🛠️ Parts Included and Tools Needed: A quick list of everything you'll need to get started.
• 📝Step-by-Step Instructions: Clear, easy-to-follow directions from disassembling your dash to securing the new Sony head unit.
• ⚠️ Special Notes: Important information and considerations for your installation.
• 🛠️ Common Troubleshooting Solutions: Quick and effective fixes for common installation and performance issues.

Table of Contents

• Important Updates
• Installation Video
• Parts Included
• Tools Needed
• Step 1: Preparing the Subwoofer
• Step 2: Installing the Left Bracket & Amplifier
• Step 3: Installing the Right Bracket
• Step 4: Disassembling the Dash
• Step 5: Disassembling Your 4Runner
• Step 6: Routing the Power Wire
• Step 7: Routing the Main Harness
• Step 8: Making Connections to Your Head Unit
• Step 9: Reinstall Your Head Unit
• Step 10: Connecting the Ground Wire
• Step 11: Connecting the Bass Control Knob
• Step 12: Installing the Subwoofer and Amplifier
• Step 13: Connecting the Power Wire to the Battery
• Amplifier & Subwoofer Settings - Reference Only
• Step 14: Testing System Functionality
• Step 15: Reassembling Your 4Runner
• Common Troubleshooting Solutions

📢 Important Updates & Notes

Update (September 2026): Factory Head Unit Installations
If you have a factory head unit, please disconnect the RCA connections and connect the two red 4-pin connectors directly to each other. Then, press the SPIN/REM button on the PWE-S8 so that SPIN is pressed IN and enabled.

Update (September 2026): Video Installation Notes
At 47:49 in the video below, a separate installation guide is referenced. That guide is no longer applicable. Please use this web-based guide for the most current installation instructions.

At 50:15 in the video, we walk through setting the amplifier. You can skip this step, as we now pre-set the amplifier settings for you before your bundle ships.

Update (February 2025): Kit Assembly:
To ensure your items arrive safely, we’ve updated the kit assembly process. Please follow Steps 1, 2, and 3 to complete the final assembly of your Alpine 4-Channel Amplifier and Subwoofer Kit from Trail Grid Pro.

🎥Installation Video

🛠️Parts Included:

• Amplifier assembly:
• Vehicle specific mounting bracket
• Alpine PWE-S8 powered subwoofer
• Alpine KTA-450 4 channel amplifier
• AudX T-Harness
• Main harness
• RCA adapters
• Power Cable
• 10 Zip Ties
• 10mm Ground Bolt

🛠️Tools Needed:

• Panel removal tool
• 10 mm socket
• 12 mm socket
• 14 mm socket
• 3 mm Allen wrench
• Ratchet wrench
• Socket extension
• Phillips head screwdriver
• Zip ties
• Razor knife
• Wire fish
• Wire brush

📝Step-by-Step Instructions

Step 1: Preparing the Subwoofer

• Take the subwoofer out of the packaging.
• Place it on a flat surface with the speaker grille facing downward.
• Position the subwoofer so that the Alpine sticker and controls are visible and facing you.

Step 2: Installing the Left Bracket and Amplifier

• Take the bracket out of the packaging.
• Place it on a flat surface as shown in the image below.

• Take the amplifier out of the packaging.
• Position it onto the left bracket.
• Make sure the gain controls are facing you.

• Using a 3 mm Allen, secure the amplifier to the bracket using the screws provided in the “Amplifier Mounting Screws” bag.

• Flip the bracket over and position it on the left side of the subwoofer.

• Secure the left bracket using the screws provided in the “Bracket Mounting Screws” bag.
• For each assembly, insert one bolt, followed by a split washer, and then a flat washer.
• Repeat this process four times.
• Tighten the Phillips head bolts, but avoid over-tightening.

Step 3: Installing the Right Bracket

• Take the bracket out of the packaging and position it on the subwoofer as shown below.

• Secure the right bracket using the screws from the “Bracket Mounting Screws” bag.
• For each assembly, insert one bolt, followed by a split washer, and then a flat washer.
• Repeat this process four times.
• Tighten the Phillips head bolts, but avoid over-tightening.

Step 4: Disassembling the Dash

• Pull the two side panels on either side of the HVAC control straight back to remove them.
• Pull the HVAC control panel straight out to detach it.
• Use a panel removal tool to remove the wire holder.
• Disconnect the wire connector from the back of the panel.
• Loosen the four 10 mm bolts securing the radio to the dash.
• Do not fully remove the radio yet, as additional disassembly is required before accessing the rear connections.

Step 5: Disassembling Your 4Runner

Remove the center console:

• If you have a manual 4WD gear shifter, twist the handle counterclockwise to remove it.
• Twist the gear shifter handle counterclockwise to remove it.
• Lift up on the shifter panel to detach it.
• Disconnect any wire connections before fully removing the panel.
• Use a pry tool to lift and remove the lower trim panel.

• Remove the two 10 mm bolts securing the trim panel containing the 12V outlet and USB.

• Pull the panel straight out to release the retaining tabs.
• Disconnect any connectors before removing the panel completely.

Remove the passenger front seat: 

• Lift the passenger front door sill plate straight up to remove it.
• Remove the plastic nut securing the passenger-side kick panel.
• Pull the kick panel straight out to detach it.
• Remove the plastic covers from the front seat bolt brackets.
• Use a 14 mm socket to remove the front seat bolts.
• Move the seat into the forward position.
• Remove the plastic covers from the rear seat brackets.
• Use a 14 mm socket to remove the rear seat bolts.
• Move the seat to the middle position and lean it back to access the underside.
• Disconnect all wiring connectors by pressing the release tabs.
• Carefully remove the seat from the vehicle.

Step 6: Routing the Power Wire

• Open the hood and secure it in place.
• Locate the spyder-wrapped power wire with an inline fuse (included in the kit).
• Start by placing the ring terminal near the positive battery terminal.
• Route the power wire along the driver’s side fender, across the firewall, and toward the passenger-side firewall grommet.
• Using a utility knife, carefully cut an "X" in the grommet to allow the power wire to pass through.
  • ⚠️Note: Many Toyota firewall grommets have both an exterior and interior membrane—you will need to cut through both.
  • Take extra care to avoid damaging any vehicle wiring while cutting.
• Use a wire fish tool if needed to guide the blue bullet connector end of the power wire into the cab.
• Once the power wire is through the firewall, pull the slack into the passenger-side floorboard.
• Secure any loose wiring in the engine bay using the provided zip ties.

Step 7: Routing the Main Harness

• Position the main harness under the front passenger seat.
• Start with the AudX T-harness end and route it towards the head unit.
• Run the harness under the carpet, directing it toward the gear shifter.
• Continue through the transmission tunnel area, moving towards the front of the vehicle.

• Remove the radio to access the connection points.
• Guide the AudX T-harness up inside the dash, routing it towards the main radio connections.

Step 8: Making Connections to Your Head Unit

Making connections to your 2010-2019 head unit:

Factory Head Unit:

• Disconnect the 10-pin and 6-pin connectors from the back of the head unit.
• Plug the male end of the AudX T-Harness into the 10-pin and 6-pin ports on the head unit.
• Attach the vehicle’s 10-pin and 6-pin connectors to the female end of the AudX T-Harness.

Aftermarket Head Unit:

• Disconnect the 10-pin and 6-pin connectors from the back of the head unit.
• Connect the male end of the AudX T-Harness to the 10-pin and 6-pin ports on the head unit.
• Attach the vehicle’s 10-pin and 6-pin connectors to the female end of the AudX T-Harness.
• Connect RCA cables to the RCA outputs on the aftermarket radio.
• Front Speakers:
  • White to White
  • Grey to Red
• Rear Speakers:
  • Green to White
  • Purple to Red
• Subwoofer:
  • White to White
  • Red to Red

Making connections to your 2020-2024 head unit:

Factory Head Unit:

• Disconnect the 10-pin connector from the back of the head unit.
• Connect the male end of the AudX T-Harness to the 10-pin port on the head unit.
• Attach the vehicle’s 10-pin connector to the female end of the AudX T-Harness.
• Use the provided remote wire T-harness inline with the AM/FM connection from the back of your head unit.
  • Disconnect the AM/FM antenna connection from the back of the head unit.
  • Connect the female end of the T-harness to the male end coming from your dash.
  • Connect the male end of the T-harness back into your factory head unit.
  • Connect the blue remote wire (female bullet connector end) to the blue remote wire from the Alpine main harness.

Aftermarket Head Unit:

• Disconnect the 10-pin connector from the back of the head unit.
• Connect the male end of the AudX T-Harness to the 10-pin location on the head unit.
• Attach the vehicle’s 10-pin connector to the female end of the AudX T-Harness.
• Use the provided bullet connectors to connect the remote turn-on wire (Blue with White Stripe) to the aftermarket head unit.
• Connect RCA cables to the RCA outputs on the aftermarket radio:
• Front Speakers:
  • White to White
  • Grey to Red
• Rear Speakers:
  • Green to White
  • Purple to Red
• Subwoofer:
  • White to White
  • Red to Red

Step 9: Reinstall Your Head Unit

• Ensure that all previously disconnected connections are securely reattached.
• Position the head unit back into the dash and fasten it using the four factory 10mm bolts.
• Do not fully reassemble the dash yet—functionality should be tested before completing the installation.

Step 10: Connecting the Ground Wire

• Use the provided ground wire to connect the ring terminal to the factory ground located under the passenger seat.
• If a factory ground bolt is not present, secure the ring terminal using the provided bolt in the pre-threaded hole under the passenger seat.
• Before securing the ground connection, thoroughly clean the grounding location with a wire brush to expose bare vehicle metal. There should be no paint, coating, debris, or other material between the ring terminal and the bare metal.
• Tighten the ground connection securely and verify that the ring terminal does not move.

Step 11: Connecting the Bass Control Knob

• If using the kit with a factory head unit and want to adjust the bass, install the provided control knob.
• Attach the bass control knob in your preferred location using the included Velcro or the Bass Knob Switch Blank Mount.
• Route the control knob wire to the subwoofer/amplifier assembly and plug the 3.5 mm headphone jack into the subwoofer.
• Use zip ties to secure any excess or loose wiring.

Step 12: Installing the Subwoofer and Amplifier

• Position the subwoofer/amplifier assembly on the floor under the front passenger seat.
  • The angled end of the brackets should face the front of the vehicle.
  • When properly aligned, the bracket holes will match the factory seat bolt locations and locating pins.

Connecting the Main Harness to the Subwoofer and Amplifier:

• Connect the White 14-pin connector to the subwoofer.
• Connect the RCA cables from the main harness to the subwoofer:
  • Red to Red
  • White to White

• Connect the Black 22-pin connector to the amplifier.
  

• Connect the bullet connector from the previously installed power wire to the yellow wire on the main harness.

• Use the provided zip ties to secure any loose or excess wiring.

Step 13: Connecting the Power Wire to the Battery

• Use a 10 mm or 12 mm wrench to remove the nut from the positive battery terminal.
• Place the ring terminal from the main harness power wire onto the positive terminal and secure it with the factory nut.
  • ⚠️Note: A small spark when connecting the ring terminal is normal and expected.

Amplifier & Subwoofer Settings - Reference Only

⚠️ Reference Only: Your amplifier and subwoofer settings are pre-set by Trail Grid Pro before your kit ships. You do not need to adjust these settings during installation. The settings below are provided only as a reference in case you need to verify or restore them.

Subwoofer (PWE-S8) Settings:

Factory Head Unit Amplifier Settings:

Aftermarket Head Unit Amplifier Settings:

Step 14: Testing System Functionality

• Power on your vehicle and verify that all components are functioning properly.
• Play a song that will run continuously for a few minutes.
• Check the Balance/Fade settings to ensure all speakers are playing correctly.

Once you have confirmed that your system is working and the gains are adjusted to your preference, reassemble your vehicle and enjoy your newly amplified system!

Step 15: Reassembling Your 4Runner

Reinstalling the Front Passenger Seat:

• Ensure the amplifier and subwoofer settings are set to your preference before reinstalling the seat.
• Secure any loose wires and align the subwoofer/amplifier brackets with the mounting holes in the floorboard.
• Carefully position the seat back in place.
• Reconnect any wiring harnesses that were disconnected during disassembly.
• Hand-tighten the four 14 mm bolts that secure the seat.
• Use a 14 mm socket to fully tighten the seat bolts.
• Reattach the plastic covers over the seat bolts.

Reinstalling Trim Panels and Center Console:

• Replace the kick panel at the bottom of the A-pillar and secure the plastic retention nut.
• Press the door sill panel back into place.
• Install the plastic trim panel below the glove box.
• Replace the panel under the dash.
• Reconnect any wiring connectors to the center console trim.
• Position the console trim and press it down to secure it.
• Reinstall the lower trim panel containing the 12V outlet and USB.
  • Secure it with two 10 mm bolts.

Reinstalling the Radio and Center Dash Trim:

• Tighten all four 10 mm bolts securing the head unit.
• Reconnect the HVAC panel wiring and press it firmly into place.
• Reattach the side trim panels, ensuring they snap securely into position.

Congratulations on installing your new Alpine 4 Channel Amplifier and Powered Subwoofer kit!

🛠️ Common Troubleshooting Solutions: Experiencing issues with your installation? Try these steps before reaching out for support.

1. Check the Connections Behind the Head Unit

If you have a factory head unit:

• Ensure all main vehicle connectors are fully seated and locked into place.
• Verify the remote wire from the amplifier harness is properly connected.
• Inspect the harness connections for any loose terminals, bent pins, or wires that may have backed out of the connectors.
• Make sure no wiring or connectors are pinched behind the head unit when it is installed.

If you have an aftermarket head unit:

• Ensure all main vehicle connectors are fully seated and locked into place.
• Verify that the RCA connections are fully plugged in.
• Check that the remote wire from the amplifier harness is connected to the radio harness.
• Make sure the subwoofer output is turned ON in the head unit settings menu.
• Verify that the front and rear RCA connections are connected to the correct outputs on the head unit, if applicable.
• Inspect the harness connections for any loose terminals, bent pins, or wires that may have backed out of the connectors.
• Make sure no wiring or connectors are pinched behind the head unit.

2. Check the Alpine Amplifier Settings

• Remove and clean the ground connection. Disconnect the ground and thoroughly clean the grounding location with a wire brush. There should be no paint, coating, debris, or other material between the ground terminal and bare vehicle metal. Once cleaned, reconnect the ground and make sure it is tight and secure.
• Confirm that the front and rear gain settings are turned low/off.
  
• Double-check the dip switches on the amplifier—the recommended settings can be found in the installation guide.

3. Check the Subwoofer Settings

• Make sure the input selector is set correctly for your head unit:
  • Aftermarket head unit: Set the input selector to REM (Remote).
  • Factory head unit: Set the input selector to SPIN, making sure SPIN is pressed IN and is not sticking out.
• Verify that the blue indicator light is on.
• Check that the gain and crossover dials are set to low/off.
• Verify the correct audio connections:
  • Aftermarket head unit: Ensure the RCA adapter from the amplifier harness is connected to the RCA inputs on the subwoofer.
  • Factory head unit: Disconnect the RCA connections and connect the two red 4-pin  connectors directly into each other.

If the RCA adapter is not connected and you have an aftermarket head unit, follow these steps:

• Locate the red 4 pin connector on the main harness near the subwoofer.
• Disconnect the male and female ends of the red 4 pin connector.
• Find the RCA adapter in the "Extra Parts" bag.
• Attach the male 4-Pin connector from the RCA adapter to the female red 4 pin connector.
• Connect the RCA's to the RCA inputs on the subwoofer.
• Play music and adjust the subwoofer gain to your preferred level.

4. Bass Knob 

If your bass knob is not working with a factory head unit, please verify the following:

• Make sure the PWE-S8 is set to SPIN.
• Make sure the RCA connections are disconnected.
• Confirm that the two red 4-pin connectors are connected directly to each other.

Please refer to Troubleshooting Step 3 for additional details.

5. Optimizing Sound Quality and Tuning Your System

Once you’ve confirmed all connections and verified that the amplifier and subwoofer are functioning properly, follow these recommendations to fine-tune your system.

• If using a factory head unit, keep in mind that the audio signal level increases as the volume is raised.
• Setting the amplifier gain too high can cause distortion or may cause the amplifier to enter protection before reaching higher volume levels.
• Gain should be used to properly match the amplifier to the incoming audio signal, not simply as a volume control.

Recommended Tuning Process:

• Turn the gain adjustments on both the amplifier and subwoofer to their lowest settings.
• Play a clean, high-quality song that will continue playing for several minutes.
• Gradually increase the head unit volume to approximately 75% of maximum volume.
• If you hear distortion, experience audio cutout, or the amplifier enters protection before reaching this level, stop increasing the volume and refer to the troubleshooting section before continuing.
• Using a small flathead screwdriver, slowly increase the Front Gain until you reach your desired output level without distortion.
• Repeat the process for the Rear Gain.
• Slowly adjust the Sub Gain to blend the PWE-S8 with the rest of the system.
• Fine-tune the subwoofer crossover based on your listening preference.

Important: Avoid continuing to increase the gain or volume if you hear distortion, popping, crackling, or experience complete audio cutout. These symptoms should be addressed before continuing with tuning.

Final Adjustments & Sound Tweaks

• If you hear distortion, clipping, popping, crackling, or experience audio cutout, stop increasing the volume or gain and refer to the Troubleshooting section before continuing.
• Adjust the EQ settings within your head unit to fine-tune the sound to your preference.
• Avoid excessive bass or EQ boost, as this can cause distortion or place additional demand on the amplifier and speakers.
• If using an aftermarket head unit, make sure the subwoofer output is turned on in the head unit settings menu.
• Make small adjustments at a time and test the system before making additional changes.

Contact Us

If you're still encountering difficulties and need additional troubleshooting support, please reach out using this contact form, and someone will get in touch as soon as possible.