I wonder what the purpose the "Road speed input" has to the system?
Is the dashboard fed the PCM? I know the car from which my GM PCM came, the dash instruments are electronci and are fed by the PCM and BCU. That is not needed in my setup but I found that the PCM also has tach and speedo outputs which are proving to be useful.
Paranoia would indicate something far more sinister :-)
The road speed input lets the ECU know whether the vehicle is moving or not.
It can then calculate idle speed and decel fuel cuts etc.
The system will run OK without the input but will run better with it hooked up.
The frequency of the speed input doesn't matter. The ecu just looks for a pulse to determine vehicle movement.
Hope that helps
Cheers
Fred