Thanks!!
RE: Speedo input I'm a bit rusty on some of the particulars since I haven't worked on my cars in a while due to back problems (yes, I'm getting to be an old timer!
) I found this page which discusses the signals coming from most vehicle speed sensors:
http://www.magsensors.com/vssapps.html
The VSS on my Fords, for example, is a Hall effect sensor which produces a digital pulse waveform. Each pulse is the same voltage, only the frequency varies with vehicle speed. All you need to do is count these pulses to get the mileage travelled, and count pulses per time to get the correct speed. I would recommend tapping this input directly for any speedometer application and getting other info like tach readouts from the ECU via OBDII.