That's quite a ambitious project you've taken on. I can only give a possible answer (but not validated) to:
The computer also sends both the VSS and engine RPM signal to the electronic steering pump's control box so that power steering works. However, I am not sure how the power steering control box handles the signals - this is why I need to figure out how the signals interact before making a final circuit.
I believe the higher speed a vehicle is going the less power steering force it requires to prevent over sensitive steering control at higher speeds. So I suspect the signal was used to vary or bypass the hydraulic pressure applied to the power steering assist actuator.
Lefty