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

20-pin 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!

Most of the wires on my harness also have printed labels telling you the purpose of each wire.  You might need a magnifying glass and/or bright light to be able to read them.

If your car is a newer model not covered by my pin-out table, the functions of most of the wires are still the same (for example, the power, ground, illumination, and 8 speaker wires are always still in the same slots).  The only differences are the functions of pins 11, 12, 13, and 19.  In general, Legacy/Outback and recent Impreza, Forester, and Crosstrek models dropped CAN bus, and added some other signals.

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

Wire nuts (the type you twist onto the end of two or more wires that you've twisted together) are not a good method for cars.  They are not designed for situations where there will be bumps and vibrations.

Posi-Locks are a good, tool-free alternative.  However, they're a bit more expensive, and harder to find.

Soldering is strongly recommended for the steering wheel control (SWC) wires.  T-taps ("Scotchloks", AKA "vampire" taps — insulation displacement connectors) 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.

Speaker wires on cars with h/k system

Some recent Subaru models have an external factory harman/kardon amplifier and speakers (you can tell by the "harman/kardon" emblems on all of your car's speakers).  The amp, located under one of the front seats in most models, or under the rear parcel shelf in 2015–up WRX and STi, drives all of the car's main speakers and subwoofer.

It had been widely thought that the OEM HUs in these cars sent line-level (low level, un-amplified) signals to the h/k amp.  However, people have found that the HUs actually are still outputting high-level (amplified) signals — the HU could be connected directly to speakers.

On the the 2009 Legacy/Outback HU models P-206UHB and P-206UNB, the manufacturer's label shows that the outputs are 10,000 ohms (instead of the typical 4 or 8 ohms).  I suspect that the OEM HUs in other car models with the h/k system have the same characteristic.

While some people have connected their aftermarket HU's amplified speaker outputs to the h/k amp without any problems, others have reported excessive "hiss" and volume levels that were too high.  So I'm now recommending that people connect a HU's line level (low level, un-amplified) outputs to the h/k amp.

To connect your new HU's line outs to the OEM h/k amp, use a 20-pin harness with male RCA plugs instead of plain speaker wires (similar to Metra 70-7553, except with the added SWC wires — I have that available).  The RCA plugs are color-coded the same as the car stereo speaker wire color codes:

  • GREEN — Left rear
  • VIOLET — Right rear
  • WHITE — Left front
  • GRAY — Right front

Plug each RCA plug into your new HU's corresponding line-level output.  Remember you will also need to connect the h/k amp trigger lead on the aux harness.

Individually insulate the ends of your HU's speaker output wires.  If your HU has a menu option to deactivate the built-in speaker amplifiers, you may find it helpful to also do that.

If you decide you would rather bypass the OEM h/k amp, I can supply "forward" harnesses to connect to the factory speaker harnesses that are currently plugged into the h/k amp.  E-mail me for more information.

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 and/or subwoofer 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.

Important: A Subaru's antenna booster amplifier must receive a full 12 Volts to work properly.  So use a voltmeter to verify that your HU supplies at least 12V.  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 or switch to a different source (aux, disc, etc.).

Ground Wire (BLACK)

Many HU manufacturers put a ring or "C" terminal 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.

Most Subarus also have a redundant chassis ground lead.  See "Chassis Ground Harness" section, below.

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.

CAN Data Bus Wires

I'm not aware of any aftermarket HU that can use these signals from a Subaru.

Some Chinese HUs include CAN wires, which some cars use for their steering wheel interface.  However, no Subaru models use CAN bus for SWCs.  All Subarus have resistive SWCs.

If you requested CAN wires on my harness 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.).

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 black ground lead on my 20-pin harness is sufficient.

If you're reusing your factory metal mounting brackets (for example, when using one of the JDM-style bezels, or combining your metal brackets with a modified plastic dash kit), there is a similar lug on the left side bracket that you can clip the factory ground harness onto.  See this post.  On recent models, the lug is at the very bottom of the left bracket (hidden when the bracket is installed).

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

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 aftermarket adapters 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.

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

I have the ASWC-1 modules available.  See this page.

I've recently learned that some ASWCs don't run the auto-detect process on the first power up out of the box.  The module will flash green once, as if it had already been programmed (instead of a longer sequence of green and red blinks it provides to confirm which wires and what HU brand you've connected).  If yours just flashes one green when you needed it to auto-program, simply press the ASWC's reset button (see instructions in the ASWC's printed manual).

If you have trouble with your ASWC and need to contact Metra's tech support, e-mail me for some things you should know before you do.

Metra's previous ASWC firmware update was v3.20, released May 5, 2014, with some significant changes.  More recently, Metra released three more ASWC updates — version 3.21 on 3/1/2015, version 3.22 on 3/19/2015, and version 3.23 on 5/5/2015.  They did not include any release notes, so I don't know what changed.

If you ordered the ASWC from me, I updated your module to the latest version just before I shipped.  If you purchased your ASWC elsewhere and it has an older version (last 3 digits of long number on white sticker), you probably want to update yours.  To update an older ASWC model, I have Metra's USB-CAB programming cable available.

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.

Chinese HUs with built-in SWC capability

Most Chinese-brand HUs (e.g., Caska, Eonon, Flyaudio, Rosen, etc.), and those without any brand can be connected directly to the SWC wires in cars with resistive SWC buttons.  These HUs have the equivalent function of a steering wheel interface module built-in, and have on-screen menus to "learn" a car's SWCs.  Connect as follows:

  • My BROWN/BLACK to the other BLACK ground wires (on my 20-pin harness and HU's harness).  If the HU's harness has a secondary black/ground to use with the SWCs, just connect that to my BROWN/BLACK (you don't need to tie those to the other grounds).
  • My BROWN/RED (Subaru pin #4) to HU's SWC input #1 (often labeled "KEY1", "A/D 1", or similar).
  • My BROWN/BLUE (Subaru pin #13, or pin #11 in some Legacy/Outback models) to HU's SWC input #2 (likely "KEY2", "A/D 2", or similar).

Find on-screen menus where you program the HU to assign a function to each of your car's SWC buttons.

Vehicle Speed Signal

Some aftermarket navigation HUs have a lead they want you to connect to your car's Vehicle Speed Signal (VSS).

CAUTION: Grounding the car's VSS wire or connecting it improperly can interfere with your car's antilock brake or traction control systems, speedometer, and other systems which use that signal.

Models With VSS On 20-pin Harness

These Subaru models include VSS on pin 19 on the car's factory 20-pin harness:

  • 2012–2014 Impreza (not WRX or STi)
  • 2013–2014 Crosstrek
  • 2014–2015 Forester
  • 2015 WRX and STi

If you ordered my harness with that wire, it will be BROWN/GREEN below the BLUE power antenna lead.

Some recent Nissan models have that signal also, on Nissan pin 18 (equivalent to Subaru pin 11).  If you ordered my harness in a Nissan configuration and included this extra lead, it will be BROWN/GREEN below the ORANGE illumination(+) 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.

Other Models

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 my post here.  That links to a thread on a Forester forum which shows the location in a 2009 Forester.  However, 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.

Aux adapter harness

Aux audio wires (on harness with plain wires)

If you ordered my aux harness with these, these are to retain your factory 3.5mm stereo aux jack.

Although the wires on my harness are securely crimped, do not pull any of the wires — hold only the bodies of the connectors.

On some HUs, you must adjust menu options to enable the aux input.  Refer to your HU's instruction manual.

Colors of the three aux wires on my aux retention harness (8-pin, 16-pin, and 24-pin):

Wire Color Function
WHITE Aux Audio Left
RED Aux Audio Right
VIOLET (or BLACK) Aux Audio Ground

Solder to a 3.5mm stereo plug or male left/right RCA plugs.

I recommend finding a short, commercially-made audio cable that has whichever kind of plug(s) you need to fit the aux input on the back of your new HU (either a male stereo 3.5mm plug, or left/right male RCA plugs).  Cut off and discard one end of that cable, leaving about 6" of cord going into the plug(s) you will use.  Then prepare the cut end and solder it to the three wires on my aux harness.

If you go with a cable with male left/right RCA plugs, those usually consist of two separate shielded cables, side-by-side.  You'll need to join the two grounds onto my single violet ground lead.

For either a male 3.5mm plug or RCA plugs, the center conductors are usually extremely small gauge and very fragile.  You can use the technique that I show in this post (#34 in the thread) to provide better strain relief:  Solder my aux harness's wires to the tiny wires, insulate the tips individually with small heat shrink, fold those back onto the outer jacket, and finally bind and cover everything with larger heat shrink.

Plan ahead and slide the final, larger piece of heat shrink over your commercial aux cable before you begin stripping its outer jacket.  Your cable should be long enough so you can slide that away from any heat.  Choose shrink tubing that is large enough to accept the wires that you'll be folding back onto the outside of the jacket.

As for the smaller heat shrink tubes that you'll use to cover the ends of the solder joints, you won't slide those on until after you've soldered those wires — to "cap" each solder joint.

I recommend folding back a little more than an inch (which is more than what I show in that thread).  Also, ignore where I talk about the Molex plug — my 8-, 16-, or 24-pin aux harness takes the place of that.

Subwoofer Line Output

Note: This is applicable to only a few particular Forester models which have the OEM odd-shaped subwoofer (and assumes you've ordered my aux harness with the OEM sub RCA option).

Plug the green RCA subwoofer plug into your HU's subwoofer output.  Even if your HU has 2 RCA jacks, the output is almost always mono (so you should not need a Y adapter).

Connect the BLUE/WHITE wire from my aux harness to your HU's amp remote turn-on lead (should also be BLUE/WHITE).

See my notes in the "Power Antenna Wire" section (above) for cautions about your car's antenna booster amp and how that requires a full 12 Volts.

Additional signal wires on aux harness

The following are the colors I usually use when you order my 16-pin aux harness with these additional signal leads:

Pin Number Wire Color Function Comments
5 BLUE/WHITE +12V remote turn-on to amp or sub Only models with OEM odd-shaped subwoofer or harman/kardon amplifier & speaker system
15 GRAY Parking Brake signal +12V when brake off, ground when parking brake lever engaged
16 BROWN/YELLOW +12V Reverse Gear signal +12V when ignition on and gear shift in reverse (same signal as used to power car's reverse lamps)

On 2010–2011 Legacy and Outback with h/k system, the amp turn-on is pin #23 on the 24-pin aux harness.

On older Forester models with the odd-shaped subwoofer and an 8-pin aux harness, the remote turn-on for that sub is pin #3 on the 8-pin harness.

Note: Parking brake and reverse gear signals are applicable only to certain cars (2013–up Crosstrek, 2012–up Impreza (not WRX or STi), and 2011–2013 Forester with CP635U1 or similar Forester models with 4.3" screen).  No other models have these signals on the 8- or 16-pin aux harness!

Reverse Gear Signal

For most Impreza, WRX, STi, Forester, Legacy/Liberty, and Outback models which do not have the reverse gear signal on a factory radio harness, you can find the reverse gear signal on a factory 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.

The car's reverse gear signal is +12V when the reverse lamps are lit (which only happens when the key is in the ON/RUN position.  For testing, you do not need to actually crank the engine.

Note:  Models may have other factory wires that are also BROWN/YELLOW, but which are not the reverse signal!  Before you tap into a wire in a different location, you must verify that it really is this signal (using Subaru's wiring diagrams, harness location drawings, and a voltmeter).  With the prevalence of airbag wires throughout cars, it is very unwise to poke around wires you're unsure of.

USB Adapter

Installation should be fairly straightforward — connect between your car's factory USB harness and your HU's rear USB socket.

Since USB "A" connectors are held together only by friction, I suggest that you devise some way to keep the USB adapter secured to the new HU's USB socket (such as plastic cable ties).  I don't recommend using tape, as that will likely lose its stickiness after a few cycles of getting hot and cold.

Multi-Function Display (MFD) Reset

If your car is one of the recent models with the Multi-Function Display and it was showing information from your OEM HU (audio source, radio station ID, artist, song title, etc.), you must reset the MFD to avoid the "Please Check Audio System" error.  Do that by temporarily removing power for a short time, using one of these methods:

  1. Remove fuse that powers MFD.  This is on the main fuse panel located in the engine bay, labeled "Back-up" (as in "memory backup").  In 2015 WRX & STi, 2014-2015 Forester, and 2012-2014 Impreza and Crosstrek, it's 20 Amp fuse #8 (by itself, near several larger slow blow fuses).  Fuse #8 also supplies power to the HU's +12V Battery lead, as well as things such as keyless entry and courtesy lights.
  2. Unplug 12-pin harness from rear of MFD
  3. Disconnect negative terminal from the car's battery

You must disconnect power from the MFD somewhere between 30 and 60 seconds.  If anyone could narrow down the minimum time to make the MFD "forget," I'd be grateful.

Retain Sat Radio Antenna

This is only applicable to cars whose factory HU has built-in XM and uses a FAKRA connector (rectangular-shaped pink plastic shroud surrounding a round coax connector).  It is possible to use the factory sat radio antenna with an aftermarket SiriusXM sat radio tuner module (such as the SXV200V1).

The inner connector in Subaru's plug is an SMB, same type as used on most aftermarket tuner modules.  It is not difficult to remove the outer plastic FAKRA shroud.  These instructions will be a bit vague, since I don't have one to work with while I write this.

The plastic shroud has a secondary lock on the bottom.  This is usually a different color plastic (e.g., white).  Use a small flat-blade screwdriver to pry that out (down).

The inner SMB connector is also held in by a plastic lance (spring clip).  There should be a place where you can insert the small screwdriver or a small blunt probe and lift the plastic latch away from the metal SMB, freeing the SMB (so you can pull the wire with SMB out the rear of the plastic shroud).

It should be possible to do all of that without breaking any of the plastic shroud (and especially without cutting or bending the coax cable or SMB connector).

The SMB connector will simply snap into the connector on the aftermarket sat tuner module.  The center pin is somewhat fragile, so make sure the plug is aligned properly before you plug it in.

© Copyright 2010–2015 by David Carter.  All rights reserved.