| Doubt if the signal from the sensor will do it, as with all inductive pulses they have both a positive part to the pulse and also a negative part and usually are quite weak pulses.
Often TTL electronics are used to condition the signal into someething more useable. Where as the Injected 900 ECU probably puts out a nice digital pulse that is likely to be handled by CMOS Electronics in the tacho.
So you would need to build a filtering circuit to eliminate the negative side of the pulse that could then trigger some TTL based circuit that could then trigger a transistor to give you a nice CMOS level output for your tacho.
You have more chance of running the tacho off the switched side of the Ignition Coil, but often this signal is to noisey for the Tacho to make sense of it
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