This works only for the Crossfire SRT-6, when driving and having the stereo on radio, not CD mode...under the lcd screen (the ten or so small square buttons) if you press the last one to the very right, and then immediately press the first one on the very left. something on the screen pops up indicating you're speed but in different measurement (have no idea why it says 450 when going 65-70 mph...anyone clarify exactly what that whole thing is about?