Ok, my Garmin unit arrived today, and it's already been stripped down, examined, and wired up temporarily on my workbench:
Pretty much everything worked as I'd expected but for the camera, which had me stumped for a bit.
Looking at the wiring diagram, you would assume that these units work just like any other car stereo, where supplying 12V to the reverse pin switches to the camera input.
Not so... After several hours of prodding and tracing things out, it turns out that pin 5 of the reverse camera connector has to be connected to ground when the unit is first connected to the constant and switched 12V supply. The OEM camera connects that pin to ground, which enables the reverse camera functionality. Without that, supplying 12V to the reverse trigger wire does nothing.
Seeing as I'm not forking out the insane amount of money that Suzuki want for the OEM camera, I modified my unit internally to work with pretty much any camera with a composite video output. The blue wire is a permanent ground to the PCB, so the unit always thinks there's a camera attached, and the reverse trigger will then switch to the camera image (it works like any other double-din car stereo):
The other two pins on that connector aren't needed for a non-OEM camera. They supply +6V to the OEM camera and in the case of a normal camera, you can just power it directly from the reverse lights.
By connecting the vehicle speed input on the G243 navigation connector to pin 18 of the G248 main harness internally (where the non-nav units get their speed signal), that means all I needed to add were two extra wires - Black one for the handbrake switch, and green one for the reverse camera. I also fitted an RCA socket on a flylead so the camera plugs straight in, and the unit is now ready to go:
And the proof it works is in this picture. As far as I can tell, I'm the only one yet to do this:
If you've got a Kizashi, SX4, or Grand Vitara with the Garmin unit and no camera, you can use these instructions to easily add a cheap reversing camera now... I'm looking in to sourcing the connectors so I can offer a completed plug and play loom.
Have uploaded an updated version of the guide pdf with info on the reversing camera.
