Rear Camera Input
The rear camera input on Subaru OEM head units requires a standard composite video signal. It is always NTSC, even in countries that use PAL for TV. The HU has no configuration option to use a PAL camera. You must choose a camera that outputs NTSC.
Most Subaru HU models add parking guide lines. There are menus in the HU's diagnostic/setup mode which will allow you to shift the location of the lines on the image (useful if you mount the camera off center). There is also an option to disable the lines. Although many cameras can generate their own lines, those are usually not adjustable. So you may want to choose a camera that does not have the lines (or where they can be disabled). Check with your camera's vendor or manufacturer before buying.
These instructions are for my 8-pin camera harness.
First Test Your Camera!
Many people have purchased cameras that did not work — either because they were dead out of the box, had the wrong video format (PAL instead of NTSC), or their signal was not compatible with the factory HU's rear camera input. See this post for an example of a camera whose signal was not compatible.
So before you install your camera, I strongly recommend that you test the camera on a TV or monitor that has a composite video input, so you can quickly find out if the camera has any problems.
Next, test your camera connected to your factory HU (via my camera harness) — again, before you spend any time installing the camera's long cable (and especially before you drill holes, cut wires, etc.). You'll want to know if the camera has any problems while it's still easy to pack up and return to the vendor (and your next camera could need different holes).
As an added precaution, especially for a camera with a limited range of angle adjustment, I suggest temporarily placing it as close as possible to your planned mounting location — use some double-sided tape, a glob of putty, a helper, or anything else you can come up with — and check the view on a monitor or your HU. The goal here is to verify that you'll be able to adjust the camera angle so that it gives you the view you want (not too much bumper or pavement straight down, and not too much sky).
If your camera is not from a name brand (Kenwood, Clarion, etc.), you might even go so far as to temporarily mount it on your license plate or wedged in your rear window and drive around with it several days to make sure it doesn't die.
Camera Detect Pin
The HU's 8-pin camera socket includes a pin for "camera detection" (pin 6). When nothing is connected to that pin, the HU decides to not enable the rear camera feature. My harness has a wire which loops back into another pin that supplies ground. So you do not need to do anything to enable the camera function besides plugging in my harness. The HU will then automatically display the camera's video whenever you shift into reverse.
Older versions of my harness have a long wire with a "fork" terminal on the enable pin. On that version, you must connect the wire to chassis ground (via a screw on the rear or side of the HU).
Camera Power Wire
If you ordered my harness with the camera power wire (pin 3), that will be RED/WHITE (mostly RED with a WHITE stripe. On my older harnesses, the stripe is YELLOW. I may also have marked that with a short piece of heat shrink tubing, labeled "6V to CAM".
This lead provides a 6 Volts power supply to the camera. Subaru OEM cameras for Forester, XV Crosstrek, and recent Legacy/Outback models work from this 6V supply.
Many aftermarket cameras will also work with a 6 Volt supply (even when the manufacturer's specs say "12V"), including the Rydeen DUO and MINy. If in doubt, test your camera from 6V. Try a good 9V battery as an easy initial test, then 6V (you can use 4x 1.5V batteries). Also be sure to test in low light. People have run across some cameras that look OK from 6V in daylight but have noticeable degradation from 6V in dark (and needed a slightly higher voltage).
If you ordered my harness with the 6V power lead and your camera will work from 6 Volts, connect the camera's positive power wire to my 6V lead. Connect the camera's ground lead to chassis ground (e.g., to a screw or bolt located on a good, clean, bare metal contact point near the camera's wire).
If you ordered my harness with the 6V lead but your camera requires a 12 Volt supply, insulate the end of my 6V lead. Use your car's reverse gear signal for the camera's power. That's also the way to go if you ordered my harness without the 6V lead. This post explains where you can tap into the reverse gear signal in the passenger footwell in Imprezas and Foresters.
If your camera requires +12V Accessory power, as some Kenwood camera models do, you'll have to determine where and how to tap into that source.
Cameras With Two Power Leads
Many cameras, including several Rydeen models, have a second branch on their RED power lead — one near the camera, and another at the HU end of their long video cable. The two leads are electrically the same (tied together somewhere inside the camera's cable).
The intention was for you to power the camera from the reverse lights (using the camera's lead at the rear of the car), and then the other red lead would be available to feed the reverse gear signal to your HU or a monitor screen.
In most cases, you can actually use either lead to supply power to your camera. If you use the front lead to power the camera, you should insulate the lead near the camera — do not try to power the camera from both leads!
Install Camera Harness
Plug my harness into your OEM HU's 8-pin camera socket. Picture showing the camera socket on OEM Kenwood Navi HUs:
Test the rear camera function before you reinstall the HU and reassemble your dash. Tip: You must turn your ignition key to the "ON" position for the reverse lights circuit to work. You do not need to crank the engine, though.
Adjust Parking Guide Lines
On many OEM HU models, you can adjust the HU's guide lines to suit your camera's position and view angle/ The lines will help you avoid hitting something behind you. They can even assist with centering your car into a parking space.
On some HUs, you can disable the lines if you prefer not to have them (or installed a camera that generates its own lines which you can't turn off).
Impreza & Forester OEM Kenwood Navigation
The Kenwood Navi in 2008–2009 models (at least those with older maps and software) do not have parking guide lines. However, I've been told that installing newer maps updates the software and adds that feature.
In newer models, you may adjust the guide lines or disable them, via a menu option within the HU's Diagnostics mode. See this thread (see instructions starting post #1, section 9, "What does the "Dealer Diag Menu" show?"). Also see my post #3 in that thread.
Non-nav Models with 4.3" Display
For Impreza and Forester models with 4.3" screen (CM631UD, CP235K1, CP335R1, CP435L1, CP635U1), see instructions in this post.
OEM TomTom Navigation
Unfortunately, the Subaru TomTom nav does not have parking guide lines.