The tacho sensor needs to be connected to pins 11 and 12 at the instrument cluster not earthed.

I don't think the later model tacho should cause you any problems. To check, just follow the tracks from pins 11 and 12 and confirm they connect to the tacho gauge in the instrument cluster.

If you are still using the TB42 engine harness you will need to run a wire from the tacho sensor into the instrument cluster and connect it into pin 11.

The yellow wire with a black trace should already be connected to pin 12 at the instrument cluster, you will just need to extend it from where the coil was to the tacho sensor.