Probably would have worked too if that yellow/blue wire was earthed. The sensor is an inductive pickup so one of the wires should go to earth.
I'm guessing the TD42 tacho/cluster has slightly different electronics to amplify the signal.
My TB45 tacho and wiring is the same as I suggested to you except I have the Dakota box to amplify the signal.
In all the conversion threads I've read, I haven't found one that was able to directly connect the TD42 sensor to the tacho.
It has worked for those who swapped their cluster for the TD42 unit.
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