Add a USB Port to Your Car

Then, you should be able to stick a stick in, and the computer (which is a stripped down laptop - to which you connect a monitor when you want to debug) that runs off the battery scans it and looks for the newest file called directions*.txt and prompts you with the first direction. You've set up some arrow keys somewhere within reach - either on the steering wheel or the dashboard and when you click the right arrow, you hear the next direction and if you press the left arrow, it takes you back to the previous one.