Thanks Mike, I didn't even think about activator having an accessory connected trigger. I got it all working now, except for some reason when activator launches the AppRadio application it crashes if I'm plugged into my Pioneer. If I'm plugged into a wall charger it doesn't crash. Anyway, I solved the issue by having activator launch Pioneer's "Car Media Player" app instead, which appears to work with the AppRadio app and it automatically switches over.
KillBackground also works, but it kills the background only. If I leave TomTom open and shut-off the car killbackground (for obvious reaso