There's a signal coming from the odo which supplies the car's speed to all the control ECUs (PPS, cruise, engine/gearbox, etc.). If this signal is modified at a common point, everthing on the system gets the same modified information.
Most ECUs don't want or need a modified signal. If you modify the cruise input, you should do it *after* the splice point in the loom, i.e., at the ECU itself and not, as is most common, at the odo end of the daisy chain.
When mine was modified by the importer it was done in that fashion and, depending on the year and model (hence software revision in each ECU) each ECU can give different characteristics.
Mine got itself a 120MPH speed limit and one other attribute which Mr Betts and I both agree is *TOTALLY IMPOSSIBLE* and, had I not seen it myself, I would have accused anyone on here of winding us all up. Whether I fed the cruise with 1:1 speed data or 5:8, it still worked over the same road speed range. It can't do that so I imagined it, but I didn't, but it's not possible, but it did it.
I just decided to stick the dash back on and forget it ever happened (would someone mind undoing this jacket with the lace down cuffs for me please?).