Installation Instructions for
Aftermarket Head Unit
with Subaru 20-pin Radio Harness

Refer to my pin-out table for Subaru's 20-pin harness.  Column "A" shows the wire colors on my harness.  When I talk about wire colors below, I'm always referring to the after-market colors (on my harness, etc.) not your car's factory wires!

Connect each wire to the corresponding wire on your new head unit's power/speaker harness.  Although the colors should match, read your HU's installation manual to verify the function of each wire.

If your installation will include a steering wheel interface module (Axxess ASWC-1, PAC Audio SWI-*, iDatalink Maestro, etc.), remember that you will also be connecting several wires from the interface module.  In some cases, you'll need to join a group of 3 or even 5 wires.  Read through all of the instructions before starting your installation.

How To Connect Wires

The best method to join wires is soldering.  This gives the most compact and reliable connections.  When joining two wires, spiral the ends around each other with the wires pointed towards each other, as shown in this guide.  To join three or more wires, spiral the first two as shown, then add each additional wire, one at a time, in a similar manner, and finally solder the entire junction.

If you're using heat-shrink tubing to insulate the connections, use tubing sized for each particular junction (you may need slightly larger diameter tubing when joining larger wires or more than 2 wires).  Remember to slide the tubing on before you begin twisting the wires together.

If crimping, insulated butt-splice terminals are best.  For each junction, use a crimp terminal of appropriate size for the number and gauges of wires that you're joining.

Soldering is strongly recommended for the steering wheel control (SWC) wires.  T-taps (or "vampire" taps) are a bad idea.

Watch out for the wires with stripes — the stripes are narrow and easy to miss.  It helps to work in bright light (daylight is best).

Insulate the ends of all wires (separately) that you don't use — on my 20-pin harness, your HU's harness, and the steering wheel control interface's harness.

Ground Wire (BLACK)

Many HU manufacturers put a screw terminal lug on their BLACK wire, since some car harnesses don't have a ground wire (so grounding to the car's chassis is the only option).  Since Subarus do have a ground wire on the radio harness, I recommend that you cut off the HU's terminal lug and solder or crimp that wire to the bare end of the BLACK lead on my harness.

Chassis Ground Harness

Most recent Subarus also have a "harness" with a single wire clipped onto a lug on the rear of the factory HU.  That is a redundant chassis ground.  The ground lead on my 20-pin harness is sufficient.

If you're using one of the JDM bezels (meaning you're reusing your factory brackets), there is a similar lug on the left side bracket that you can clip the factory ground harness onto.  See this post.

Otherwise use a wire tie or tape to secure the factory ground harness from rattling.

Constant Power Wire (YELLOW)

Some Clarion HUs (and possibly other brands) have two YELLOW power wires on the main power/speaker harness.  One or both wires may have an in-line fuse holder.  You will need to connect the ends of both wires to the YELLOW wire on the 20-pin harness.  Do not remove any fuse holders.

Power Antenna Wire

All Subarus after about model year 2000 (including all that use the 20-pin power/speaker harness) have an antenna booster amplifier.  This amplifies the AM and FM radio signals, to compensate for the smaller/lower antennas on recent models (foil on the rear glass, or stubby antenna on the roof).

The booster amp is powered from a pin on the radio harness (pin 9 on the 20-pin harness — BLUE wire on mine).  You must connect this wire to a source of +12V or your AM/FM radio will suffer from diminished reception.  Options:

  1. Best option:  If your new HU has a BLUE lead (labeled "AUTO ANTENNA", "POWER ANTENNA", "ANT.CONT", "ANT REM", or something similar), connect that to the BLUE lead on my harness.  This will activate your car's antenna booster amp only while you listen to AM/FM.
  2. If your new HU does not have a separate power antenna lead, most do have a BLUE/WHITE lead (labeled "REMOTE TURN-ON", "REMOTE OUTPUT", "P.CONT", "REM OUT", or something similar).  This will activate your car's antenna booster amp whenever the HU is on, even when you switch to CD or AUX input.
  3. If your new HU does not have either of the above, connect my BLUE lead to my RED +12V Accessory / switched lead.  This will power your antenna booster amp whenever you turn the ignition key to ACCessory or ON.

See footnotes (K) and (L) on my Subaru 20-pin pin-out page.

Some HUs may have a BLUE wire, a BLUE/WHITE wire, or both.  A few HUs don't have either wire.  Check your HU's installation instructions!

If your HU only has a BLUE/WHITE wire, it is OK to use that for both your Subaru's antenna booster and the turn-on signal for speaker amplifiers.  HUs will have a maximum current rating that they can supply on this output (typically 250 or 300 mA).  Check your HU's and amplifier's documentation (or ask the manufacturers) to make sure you don't exceed that rating.  A Subaru's antenna booster draws about 50 mA.

However, the car's antenna booster amplifier must receive a full 12 Volts to work properly.  So verify with a voltmeter.  If you see less than 12V, you'll have to switch to option #3.

If you are also installing an accessory device that connects to the AM/FM antenna (such as a traffic data receiver or TV), you may want to use option #3 so that the device can get reception even when you turn off your HU.

AM/FM Antenna Cable

If your car requires an antenna adapter, be aware that the coax wires and crimps on your car's factory antenna plug and my adapter are somewhat fragile.  Do not pull any of the wires!  Hold only the plastic connectors  There is a release button on one of the narrow sides of the car's plug.

On 2010–2011 (and some later) Legacy/Outback models, the car's antenna plug is behind a trim panel near the floor.  You'll need to access that before you can remove the factory HU.  See this thread.

Illumination Control Wire

Most HUs have a wire to control the brightness of their illumination.  The dimming is two-stage: The HU will be at full brightness during the day, and slightly dimmed when you turn on your car's headlights.

If your HU has a wire for "Dimmer" or "Illumination Control," connect that to the ORANGE wire (pin 1, Illumination +) on the 20-pin harness.  This wire is +12V whenever your headlights are on.

No HU today that I'm aware of wants to see a variable voltage on its illumination control wire — the HU's backlights are not able to vary gradually in tandem with your car's instrument dimmer knob.

The HU's dimmer wire may be ORANGE or ORANGE/WHITE.  However, some HUs have no dimmer wire at all — some have no dimming capability, and a few recent models use an ambient light sensor or GPS time and location.  Some HUs even have an ORANGE/WHITE wire that is not for illumination.  Check your HU's installation instructions!

On HUs that have a dimmer wire, most also have a related menu option for "dimming." Be sure to enable that option (set it to detect the voltage on the dimmer wire).  See your HU's user manual for details.

Connecting SWC Interface Module To Car

Since my 20-pin harness includes the SWC wires, you won't need to tap into your car's factory wires.

Connecting the Axxess ASWC Module

See ASWC guide for Subaru-specific instructions to install the Axxess ASWC steering wheel interface.

I have the ASWC-1 modules available.  E-mail me for details.

Other SWC Modules

See the instructions for your particular module.  In general, you will make the following connections:

  • SWC Interface Module's RED wire to the other RED wires (HU and 20-pin harness).  So this will be a junction of 3 wires.
  • Module's BLACK wire to the other BLACK ground wires (HU and 20-pin harness)
  • Pin 14 (BROWN/BLACK) on my 20-pin harness to the other BLACK ground wires.  So you will have at least 4 ground wires joined together.
  • Module's SWC input wire(s) to the SWC wires on my 20-pin harness

You'll need to make additional connection(s) between the module and your HU's "wired remote control" input.

Vehicle Speed Signal

2012–up Crosstrek and Impreza (not WRX or STi) and 2014–up Forester include a lead with the Vehicle Speed Signal (VSS) on pin 19 on the 20-pin harness.  If you ordered my harness with that wire, it will be BROWN/GREEN below the BLUE power antenna lead.

If your new HU requires the speed signal, connect the HU's lead to my VSS wire.  Otherwise, insulate the end of my VSS wire.  CAUTION: Grounding the VSS wire or connecting it improperly can cause problems with your car's antilock brake or traction control systems.

On other Impreza and Forester models (2008–2014 WRX and STi, 2008–2011 Impreza, and 2009–2013 Forester), you can find VSS on a factory harness in the passenger footwell.  See this thread.  That shows the location in a 2009 Forester, but the factory color and location is similar across all of those models.  In Impreza/WRX/STi, you should be able to see the harness with the VSS wire without having to remove any panels.  Be sure to see my post further down in that thread with the large annotated picture and some additional tips.

Reverse Gear Signal

A few recent models include the reverse gear signal at pin 16 on the 16-pin aux harness.  If you ordered a harness from me with that wire, it will usually be BROWN/YELLOW.

For most Impreza, Forester, and Legacy/Outback models, you can find the factory reverse gear wire in the passenger footwell, in a location similar to the one shown in this thread.  The factory color is BROWN/YELLOW across all models and years.

CAN Data Bus Wires

I'm not aware of any aftermarket HU that can connect to these wires.  If I sent you a harness that includes these wires and you won't be using them, insulate the ends (individually).

If you're keeping your stock HU and using a separate pair of forward/reverse harnesses to connect other aftermarket gear, join the respective CAN wires between the two harnesses (pin 11 to 11 and 12 to 12).  The pair should be twisted.  Tip: Join the CAN wires first (before any others) and then twist the two harnesses to twist these two wires.  Then continue joining or making your connections to the remaining wires (power, speakers, etc.).

© Copyright 2010–2014 by David Carter.  All rights reserved.