The problem is not with the tom-tom car Kit or the dual external GPS. The problem has to do with iOS 6 privacy settings. I have an iTouch 4 and I been having the same problem with my GPS. I'm using the tom-tom app and the tom-tom car Kit. The solution for getting the GPS working again is. First shut down the tom-tom app or what ever app you're using. Now go to settings And General and then scroll to the bottom and tap reset. Now tap Reset location and privacy. Now load your tom-tom or navigation app And it should prompt you to turn on location service again, Say yes. Now under location services you should see The tom-tom app or the navigation app you were using and slide it to on. Now Your tom-tom app should be working correctly now, But the catch is it's only going to work until another program ask to use local services. It is definitely 100% an error an iOS 6 Privacy settings. I have no idea why it does this but you can reset and it'll work every time.
Today I received an email from Dual which simply fixed the problem with the external bluetooth gps receiver!
1. Turn bluetooth-device off
2. On iOS device go to Settings->Bluetooth and find your external gps device, tap on the blue arrow, than tap on "Forget this device"
3. Close all applications
4. Hold power-off-button an swipe to shut down your iOS device
5. Turn it on again
6. Turn on your external Bluetooth GPS-receiver
7. Go to Settings->Bluetooth find your gps-receiver an tap on it to pair
8. Here we go! GPS-receiving should work again!
Thanks you guys at Dual!