Nippon Denso 503

Hello everybody,

I currently have a Rotax 503 with a points ignition system, and I recently bought a second-hand Nippondenso ignition kit to improve reliability. During installation, I have two yellow wires already connected to my voltage regulator, but I have one black wire left and I'm not sure what to do with it. Does it need to be connected to ground?

If so, that means I have no wires left to connect to my instrument for RPM reading, unlike my old system which had a dedicated green wire for that purpose. So how can I get the RPM signal to display on my instrument?

Thank you for your help