I'm doing a bit of a custom bike based on my 1999 Aprilia RS50 and one of the NSR250 MC16 things I'm using is the 3-spoke front wheel and the speedo drive since I need a speedometer for the street.

RS50 has analog gauges with rotating cables for the speedo and tach. Since there is a 99% chance that the RS50 speedo won't work with the NSR250 drive, I'm thinking of just using the full MC16 gauge cluster. I assume that the lights and stuff should be simple enough, but for the gauges themselves:

Speedo - Should work 100% since it's the same wheel, drive, tire, etc.

Temp gauge - Could work without any issues, but I assume that I will need to swap the sensor for the NSR one, probably will have to adapt it at the cylinder, but shouldn't be an issue.

Tach - This is where it gets difficult, the RS50 has a rotating cable and NSR is fully electric. Looking at the wiring diagrams on the Tyga website, I assume it's wired similarly to the temp gauge, with 1 wire for ground, 1 for power, and 1 for sensing the RPM.

The question is how does the tach "see" the RPM? Is it purely from the BY wire being connected between the CDI and the ignition coil or is there anything else going on? Is it based on the voltage between the CDI and the coil?

Would appreciate any advice on making it work, I know that I could just go with aftermarket digital gauges, but I find them to be a bit boring and want to keep it as a last resort.

Attached, the wiring diagram and the ignition for the RS50 below.