For the last few weeks I have been helping my son install a Garmin GVN 53 into his Holden Commodore VE SSV using the inbuilt colour LCD.
The task was to install a Garmin 3D GPS with text to Speech (spoken street names) and RGB video output using the Holden Colour LCD screen for around $1.2k. The composite input using the aux switches off at around 3kMPH so this was not suitable. Plus the resolution of the composite video is not flash. The Holden LCD also does not support a touch screen so a unit with a remote had to be used.
The Holden sat nav units are $2.5k when ordering a new car or about $3.5k to $4k fitted aftermarket! The Holden unit uses a DVD to load the maps and has a terrible 2D screen and no text to speech. Its like buying ten year old technology at "skiming" prices. The VDO unit was similar but at $2.5k. The HiTV unit comes in around 2.0k and uses the factory radio knobs but has poor 2D/3D map displays with no text to speech.
We therefore purchased a Garmin GVN 53 from Octapc with the 09 maps ($0.6k without maps and $0.85k with maps). Made a custom harness so that we had a RGB output from the GVN 53. Sourced an interface (GMLAN Module) so that the Holden LCD screen will activate when the Sat Nav button is pressed. This required a logic signal to the GMLAN to tell the radio head unit to switch on the RGB LCD input.
Then we designed and built a mute interface between the GMLAN module and Garmin GVN 53 so that the factory sound system dropped in volume and permitted the Garmin to talk using the factory speakers.
After a number or prototypes and testing its completed. A demo of the completed project can be seen at: http://www.eftel.net.au/~jdiz/output1.avi
We are now thinking about an IR interface between the Garmin and Holden Radio buttons but the remote on the Garmin is very easy to use as it is the same as using a telephone to send SMS messages. Plus the remote only uses one button for most commands so it is very easy to use.