Digital Dash Reprogramming
I think I have it figured out. The Data+ and Data- pins are a serial communications port. All I have to do is figure out what the baud rate, stop bits and parity are and I think I'm on my way.
I talked to a guy yesterday in Virginia that offered to reprogram my odometer for me for the slight cost of ... are you ready for this? $350!!! I said I would get back to him. (Yeah, right) Then he told me that a customer had brought in a Ford with a digital dash that was reading 299,999.9 and wouldn't go any farther. He seems to think that there is a limit of 300,000 miles on the odometer. Anyone else heard this? Since my wife's car already has 262,000 miles on it I don't think that I would want to program it to read actual miles if that is truly the case.
As far as the top speed goes here is my opinion on what is going on. The GenIII SHO has an analog speedometer that is controlled by a digital signal from either the VSS (according to my prints) or an ABS sensor (according to some GenIII guys) THe GenIII speedometer also drops out at a certain speed, I think it is around 125 or so. The digital dash is controlled by the VSS also and I think what is going on is that the pulse train is so fast at high speeds that the dashboard is subjected to "sensory overload" and cannot keep up. This might also be the reason that the tachometer will read to about 6800 and then jump to 7000.
I dismantled my parts dash yesterday just to see what all is inside and discovered that it is truly three different modules and a power supply board. It would be no big deal to swap in a different speedometer module IF there were one that actually read above 125. The downside is that there aren't any of the police dashboards that had a tachometer so that would be a major loss to me.