.but B and C should be the same signal. both come from the coil negative. so i should be able to use either one of them, using a 1000 ohm resistor on the red wire or none on the y/b wire
apparently it seems to be that the C wires signal is not strong enough i've been told.
freely translated:" De kabel van je tellerhuis komt uiteindelijk van dezelfde plek af. Bij die 3-stekker is de rode de min, de middelste de signaalkabel voor je toerenteller. Probleem schijnt te zijn dat die signaal kabel soms geen sterk genoeg signaal geeft."
The cable of your instrument cluster eventually comes from the same place. At the 3-plug the red wire is coil minus, and the middel one (Y/L) the tacho signal wire. The problem appears to be that that signal cable sometimes doesn't give a strong enough signal.