I am in the process of swapping out my 919 engine for a 2005 CBR1000 job, wiring is pretty much sorted with the exception of the speed sensor. I am not using the factory clock so this means that the speed sensor has the following:
- 12V power feed from the fuse box
- Ground wire
- Pink wire going to the speed input of the ECU

Normally the factory clocks have a 5V output on the same pink wire that goes to the ECU & speed sensor, since I am not using the factory clock I figure I will need a 5V rail sitting on this wire which I tried using a 5V voltage regulator but it doesn't seem to work. If I dummy up the factory clock with its 5V output on the pink wire and rotate the prop shaft I get the 5V rail going high and low on my oscilloscope which is great as that is what it should be doing, however if I supply the 5V rail via the regulator it stays at a constant 5V when rotating the propshaft (which to be honest I figured it would do).

Do I need to fit a pull down resistor between the 5V rail and ground?

I think you need a pull up resistor to 5v on the pink line, so it will float hi.
then the sensor takes it to ground, giving the lows