28-pin Aux/SWC Retention Harness
for Subaru, Scion, and Toyota cars

2012–up Impreza, WRX, STi, Forester, Crosstrek *
2013–2014 Legacy & Outback *
2013–up BRZ
2012–up FR-S & GT86
and many other recent Toyotas

* Cars with OEM Fujitsu Ten navigation head units

Allows you to retain your car's factory 3.5mm aux jack,
audio steering wheel controls, and other signals
without cutting or splicing any factory wires!

Picture of Subaru 28-pin aux retention harness
(Click to see larger annotated image)


  • Retain your car's factory 3.5mm stereo aux jack when you install an aftermarket head unit

  • Retain audio steering wheel controls (SWCs)

  • Retain car's reverse gear and speed signals

Product Description

In recent Subaru models with Fujitsu Ten navigation, as well as many recent Toyota models, the factory HU has a 28-pin socket on the rear for its stereo aux input, Bluetooth microphone, SWCs, and other signals.  A factory harness connects from the back of the HU to those other things.  The white 28-pin connector on my aux adapter fits the end of the factory harness that is (or was) plugged into the back of your factory-installed HU.

Most cars that use the 28-pin connector for aux also have leads for Vehicle Speed Signal (VSS) and the reverse gear signal on that harness.

When you order this harness, it is important that you tell me your car model and year, and your OEM HU model, so that I can confirm you're ordering the correct version for your car.

Harness includes the following:

Aux RCA plugs

Left+right male RCA plugs, to retain your car's factory 3.5mm aux jack.  You'll plug those into a rear aux port on your aftermarket HU.  If your HU's aux port is a 3.5mm socket, you'll need to add a 3.5mm-to-RCA adapter.

VSS Lead

~6" (15 cm) lead for the car's Vehicle Speed Signal (VSS).  Many navigation HUs can use this signal for dead reckoning — to permit (or improve) position tracking during times that you have poor or no reception from GPS satellites (e.g., while in tunnels, large parking decks, mountain canyons, urban canyons, heavy trees, etc.), as well as instances when the HU is acquiring satellites after being off for an extended time.

Reverse Gear Lead

~6" (15 cm) lead for the car's Reverse Gear signal (+12V when ignition is 'on' and gearshift is in reverse).  HUs will need this if you connect a rear view camera.  Some navigation HUs will also use the reverse gear signal (in conjunction with VSS) for dead reckoning (see previous section).

Note: FR-S models usually do not have the reverse gear signal present on the factory 28-pin harness.  If your new HU can use this signal and you'd like to connect it via the standard factory pin location, I may be able to supply a separate wire with the proper terminal you can easily snap into the empty slot on your car's 28-pin harness plug.  E-mail me for details.

Audio Steering Wheel Controls (SWC) Leads

Three ~6" (15 cm) SWC wires.  Connect to a steering wheel interface module (or directly to a HU that has the equivalent functionality built-in).  See details on the appropriate "parts needed" page for your car model.

If you order this harness along with an Axxess ASWC-1 module, I can optionally include an ASWC harness connected to this 28-pin harness, instead of the 3 SWC wires.  That will save time — you'll only need to connect the ASWC's ground and +12V leads.  Only available for Subarus with Fujitsu Ten navigation, and Toyotas.  No extra charge for this option — just let me know before you place your order.

I also offer a version of this harness without the SWC wires, for BRZ, FR-S, and GT86 models (which don't have audio controls on the steering wheel).

Signals not included on this harness:

OEM Bluetooth Microphone

For the Bluetooth phone feature, your car has a factory microphone hidden behind the map light cluster.  The mic is in a small module with an amplifier circuit.  The module's audio output is not like the signal from an aftermarket HU's mic.

I have not heard from anyone who has documented a good way to interface the OEM mic to an aftermarket HU.  You should plan to use the mic that comes with your new HU.  You might even find that you sound better to your callers by placing your mic in a location different than the factory mic.

Amplifier Remote Trigger

None of the models covered on this page have an amp trigger signal on the 28-pin harness.  On cars with an OEM external amp for the main speakers, the amp trigger will be on the 10- & 6-pin power/speaker harness.  See 'parts needed' page for your particular car year and model.

OEM USB Socket

The OEM USB socket connects to the HU via a separate harness, not the 28-pin harness.  See 'parts needed' page for your particular year/model.


$13 (harness with aux RCA plugs, VSS, reverse gear, and 3 SWC leads)

$9  harness with aux RCA plugs, VSS, and reverse gear leads)

Click here to see ordering instructions