Since you have a three wire speed sensor you may want to try this. Hall Effect sensors are able to detect slow moving and stationary teeth. Jack the rear wheel off the ground. Place the bike in neutral. The VSS sensor has 3 leads which are 1) 12 volt supply,, 2) ground , and 3) sensor out. Take a DC voltmeter and place it between the Grd and "sensor out" pins. With ignition turned ON, you should be able to rotate the rear wheel and see the meter swing from Zero volts to +5 volts, back to Zero back to +5 volts over and over again. The voltage swing will be either zero to +5 or maybe zero to 9 volts, but it will be at LEAST 5.0v or some voltage greater than 5 volts.
All pickup and speedo wires must remain hooked up while testing. Of course 1st verify you do have 12Volts on the Vss pickup. Then place your meter on the other 2 pins.
The key is:
Is the voltage greater than 5 volts DC & is it a clean swing from +5 to Zero to +5 to Zero over & over etc. (in other words a clean square wave from "0" to supply rail or +5)
See what you read.