So I traced the green and red wire back to the neutral diode. I don't know how you test one of these but it had continuity between the terminals. I connected a small piece of wire where the diode had been, to create a direct connection and the bike now turns over on the button.
Do I need this diode? Even without the diode it turns over only in neutral...

I'd be greatfull If anyone can shed any light on this thanks.