Cars with the following factory-installed Head Units (radios) find number printed on face:
CF425LM, CF525SM, CF605UL, CF625UM,
If your car has the OEM harman/kardon amplifier and speaker system, see this alternate guide for cars with h/k.
If your car has a different HU, check my other 'parts needed' guides). E-mail me if you can't find an appropriate guide or if you have one of the above HU models but do have the h/k amp and speakers.
Power/Speaker Wiring Harness
All of the above models whose OEM head units (radios) have built-in USB and Bluetooth (i.e., steering wheel includes Off-hook, On-hook, and Talk buttons) use Subaru's 20-pin harness for the power and speaker connections to the HU. You will need my 20-pin "forward" harness with 3 SWC wires ($12, link).
You'll need to solder or crimp my harness to your new HU's power/speaker harness, creating an adapter that is mostly "plug-and-play." See my Subaru 20-pin HU installation guide.
Vehicle Speed Signal
On these models, the factory 20-pin power/speaker harness includes a wire on pin #19 which provides the Vehicle Speed Signal (VSS). A few aftermarket navigation HUs can use this signal. If your new HU needs it, I can include a corresponding wire on my harness for an additional $1 ($13 total).
Steering Wheel Interface Module
The SWC wires on my harness are only part of the solution that saves you from needing to splice into factory wires. However, most aftermarket HUs also require a steering wheel interface module either the Axxess ASWC (by Metra), one of the various SWI-* models from PAC Audio (SWI-PS, SWI-JACK, etc. different models depending on your new HU's brand), or iDatalink Maestro, etc. More people prefer the ASWC.
Many Subaru owners have installed ASWCs and given rave reviews. In most cases, it programs itself and is ready to go a few seconds after the first power up. You can also manually program it if you want to reassign any buttons. Installation is much easier than with the PAC modules.
I have the ASWCs available. See this page: Axxess ASWC-1.
To install, you will need to solder (recommended) or crimp some of the interface module's wires to my 20-pin harness and your new HU's harness. I can't pre-wire the harnesses for you, since you will need to combine with your new HU's harness.
Retain Factory Aux Jack
Your factory HU has a 16-pin socket on the rear for its stereo aux input. A factory harness connects from the back of the HU to the back of the 3.5mm aux jack in your armrest center console. That harness has proprietary plugs at both ends. The harness only handles the aux socket not USB. See more information about USB below.
I make an aux adapter harness you can use to retain your factory aux jack with an aftermarket HU. See this page: Subaru 16-pin aux harness. The white 16-pin connector on my aux adapter fits the end of the factory aux harness that is (or was) plugged into the back of your factory-installed HU. My aux harness retains the stereo aux jack only, not the USB socket.
Car models covered by this guide do not have any additional signals on the car's 16-pin harness (i.e., you do not have the parking brake or reverse gear signals there).
Retain Factory USB Socket
Your factory HU has a socket on the rear for its USB input. A factory harness connects from there to the back of the USB socket in your armrest center console. That harness has proprietary plugs at both ends. The harness only handles the USB socket not aux.
20142015 Forester and 2015 WRX/STi models require a Toyota USB adapter (Metra AX-TOYUSB or PAC Audio USB-TY1). I have the Metra AX-TOYUSB available for $12. See this page: Toyota USB adapter.
The socket on the USB adapter fits the end of the factory USB harness that is (or was) plugged into the back of your factory-installed HU. Opposite end is a standard male USB "A" plug (which you'll plug into your new HU's rear USB input). Length of the cable is ~6.75" (170 mm) between the two connectors.
Before Ordering Aux and/or USB Adapters
Study the connection diagrams in your new HU's installation manuals. With the cables and interface adapters required for some phones or iPods, it's sometimes not practical to retain your car's factory aux or USB sockets (due to the physical layout of all the pieces).
Older iPods sometimes use an interface cable which splits out into two plugs at the rear of the HU one to plug into a USB socket and the other into an A/V aux input (4-pole style, with both audio and video). Your car's factory 3.5mm aux jack supports stereo audio only it will not support video for an iPod video cable. So if you plan to use that kind of iPod cable, you may not want my aux harness. See this post for pictures and more information.
Also note: older Pioneer AppRadio models SPH-DA01, SPH-DA02, SPH-DA100, and SPH-DA210 do not have any aux inputs! The newer AppRadio 4 (SPH-DA120) does have an aux input (finally!). I'm not referring to other recent Pioneer models with AppRadio mode.
If you're in doubt, check your HU's installation manual to see whether yours has any rear aux inputs.
Retain OEM Subwoofer
If your car has the rectangular-shaped OEM accessory subwoofer under either of the front seats, similar to this:
...or one of the OEM accessory subwoofers made by Kicker (in the trunk or rear cargo area), those types of subs will work with an after-market HU without any modifications or special wiring needed. All of those subs have a T-harness which taps power, ground, and the front speaker outputs from the radio's power/speaker harness. See this post for details (post #4 in my 'Subaru stock HU Info' thread on NASIOC).
Can't Retain OEM 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 (see this thread). The module's audio output is not like an aftermarket HU's mic. Nobody has documented a good way to interface the OEM mic to an aftermarket HU. See this thread for one attempt. Unless you're especially skilled at analog electronic circuit design, you should plan to use the mic that comes with your new HU.
Multi-Function Display (MFD)
Recent models with the new dash design have a Multi-Function Display (MFD) at the top of the dash, above the head unit and A/C vents.
On some models, the MFD displays information from the HU (audio source, radio station, artist, song title, etc.). When you switch to an aftermarket HU, you will loose that feature, since it requires a proprietary data interface (which no aftermarket HU has or is likely to have). However, all other (non-radio) data screens on the MFD will continue working as before.
Some models have an OEM camera shown on the MFD. When you switch to an aftermarket HU, your MFD will continue to display the OEM camera (no changes or modifications necessary). If you would prefer to have the OEM camera redirected to your new HU instead of the MFD, see next section.
When you install your new HU, you must disconnect power from the MFD for more than 30 seconds, to make the MFD "forget" it had ever seen your factory HU (otherwise the MFD will complain that the OEM HU is missing). See the MFD section of my installation instructions for details.
Redirect OEM Camera from MFD to