Does your unit have a mini USB jack in the rear? If so, this may be for you.
The instructions below worked for a Kenwood 6140 in dash unit. It may work for yours too.
Kenwood in-dash units which utilize the Garmin Navi:
Use a 3 foot mini USB cable plugged into the rear of your unit with the other end in the glove box. Put a cap over the end in the glove box so it won't short out with any other wires. Then, it's easy to pull the wire out of the glove box and plug it into your laptop for updating.
1. Make sure your car battery is in good shape or you'll have to run the engine.
2. Turn your car key to accessory and let your Kenwood boot up.
3. Then plug the USB into your laptop.
4. The screen on your Navi will then ask "mass storage or Garmin mode" Use mass storage for updating maps or Garmin mode to use Garmin's Web Updater, as long as you have an internet connection.
5. Once in mass storage, proceed to update maps using the instructions below.
Be advised that the USB cables that are already in your glove box won't work. These are used for Ipods and thumb drives. You must plug your own mini USB cable into the rear of the unit where a dealer will tell you that this is where the optional FM Traffic Receiver plugs into.
1. Connect your device to the computer.
2. Go into the Nuvi files located in the Garmin folder and backup the file named “gmapprom.img” to your computer.
3. Delete the “gmapprom.img” file from the device.
4. Copy the unlocked “gmapprom.img” file that you downloaded into the device. (this copy proceedure could take up to 45 minutes to accomplish)
5. Restart your device and check your map info via : Tools>Settings>Map>Map Info.
Hope this helps!