my factory tacho works fine and I did not need to add any wires to the alternator.
Perhaps my alternator is different.
I was told that a module was installed for speedo and tacho - sounds plug and play to me.
You shoudl call Killer Kustom Kables in Qld as they do wirinf looms for these all the time.
my engine came out of a 1991 GQ wagon - factory auto model.