how does -FakeData work?

How does the FakeData switch work? I have it on cause I'd like to test the compass and GPS speed with my new skin but it doesn't move, do I have to tell it to start or something? Is there an easier why maybe a mod that I can change the values for those vars? I don't mind writing a simple loop with a 0-200 increment to make sure it's all working. Just no idea what vars to set using vbs, would be nice though. Thanks for any help anyone can provide.

Go into Settings and then navigation. If you look in the GPS Serial Port connection there is one that says blah blah blah .txt Just change it to that and then you'll start seeing it move around (i think its in texas)

Thanks!