Does anyone know what function the instrument cluster has on the speed signal coming from the speed sensor? Is it purely to apply a pullup of 5v so that the ECU and TCM can interpret the signal? or is there something more sinister, like preventing odometer fraud or changing the signal?

There is no prevention, it uses square wave.
However it'll only go forward.
So you can clock it to zero, but hold on, It'll take a while at 5v.


There is other ways, but require industry's equipment, you can read the eeprom, and even alter if you know what your looking for, but why bother?

sorry I think you may have misunderstood. I want to remove the instrument cluster from my project car and use a 5v pullup resistor, unless of course the instrument cluster does something else. Also does the VSS have to receive an 8v supply or can it use 12v?