I'm with techdude, the reverse regulator isn't a regulator at all, it's a diode pack. Pulling in the clutch lever provides an alternative ground path for the reverse relay rather than the neutral position of the gear position switch. If the neutral light is illuminated it indicates the gear position switch is OK. The check for this part of the circuit is to ensure the bike is in neutral, side stand up, clutch lever pulled in the bike should start. If it does then put the side stand down and see whether it stars. If no, then the section from the reverse regulator to the gear position switch has a fault. (Including the regulator.) Firstly check it's connector, secondly check the cable between the regulator and the gear position switch then suspect a fault within the regulator. I say firstly check its connector and the cable because you said your fault developed over time and diodes usually fail quickly - but not always, they can fail over a period.
If you are electrically able, it's possible the wire a single diode externally to the reverse regulator pack to jump the failed internal one. Good luck with it.
Last edited by JW.; 01-04-2017 at 02:44 PM.