Overview
Several recent Subaru models have a factory head unit made by Kenwood — the type with the full-size touchscreen, pictured here:
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The navigation HUs in some 2008–2012 Legacy/Liberty/Outback look a bit different, but they are actually based on similar hardware.
All of them have a "secret" line-level output for a subwoofer that is not used in most cases. The HU has on-screed controls to adjust that sub output. See this thread on NASIOC. They also have unused pins for a video output.
Some non-nav 2010–2013 Legacy/Outback HUs also have the sub output (though I'm not sure which models). The non-nav HUs lack the on-screen controls.
This guide details how to add my custom cable with RCA jack to the vacant subwoofer pins on the factory harness.
Remove the Navi HU
Search online for guides to remove the factory HU. See post 1 of my 'Subaru stock HU info' thread on NASIOC here for links. Tip: With the Kenwood Navi in Imprezas and Foresters, if you tilt open the screen (as you would to eject discs), you'll be able to easily grab the back of the dash bezel that surrounds the HU to pull it off of the dash.
Factory 24-pin nav harness
See pin-out table for the 24-pin Navi harness in Imprezas and Foresters here (2nd half of post #11 in that thread). In Legacys and Outbacks, many of the pins have the same functions (although with different factory wire colors).
Pin numbers
Close-up pictures of the 24-pin nav harness in a 2008 STI:
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Looking at the back of the shell (factory wires pointing towards you), the pin numbers go:
---top (w/thumb latch)---
12 11 10 9 8 7 6 5 4 3
2 1
24 23 22 21 20 19 18 17 16 15 14 13
bottom (side with pin retention latch)
Inserting and extracting wires
See this guide for instructions on how to insert and extract wires from a factory harness plug.
Double-check the pin position before inserting! Although it's possible to extract a pin, it can be difficult. It's much better to get it right the first time!
Add subwoofer RCA cable and remote wire
Be careful — the pins on the wrong end (1, 2, 13, 14) are also vacant.
My RCA cable has 3 leads. Two are black and both of those are connected to the shield of the jack (ground). You will be using the second of those leads to ground the Navi's inverse polarity output (which will increase the loudness of the positive output).
Insert the RCA jack's leads as follows:
| Pin | Description | Wire Color |
| 11 | RCA jack ground | BLACK (one of two) |
| 12 | RCA jack center lead | WHITE |
| 23 | Amp remote turn-on wire | BLUE/WHITE |
| 24 | RCA jack ground | BLACK (one of two) |
(see link to "Inserting wires," above)
Avoid pulling on the RCA cable. Hold only the connector bodies.
On some subwoofers and amplifiers, you may need to use an RCA Y-adapter to connect the sub out to both of the amp's left and right inputs.
Connect the BLUE/WHITE lead to your amp's remote turn-on input. This lead may also be used for an amp for the main speakers.
Add video out RCA jack
Insert the RCA jack's leads as follows:
| Pin | Description | Wire Color |
| 13 | RCA jack center lead | YELLOW |
| 19 | RCA jack ground | BLACK |
(see "Inserting a wire," above)
Replace factory parking brake wire
Extract the factory wire from pin 4 (see instructions above for "Extracting a wire"). The wire color is GRAY on USDM Impreza and VIOLET/RED on USDM Forester models. I think it is also GRAY on EDM and AUDM 2008–2009 Legacy/Liberty/Outback models.
Insert the new replacement pin/wire that I sent you.
Connect the end of the new wire to chassis ground (use a screw on the rear or side of the Navi HU). You might want to first crimp on a "fork" or ring terminal before you start.
Insulate the end of the factory brake wire (the terminal you extracted).