Tach adapter? It's need is unknown until you install the ign. system. I first installed Crane's XR700, then a Hi6S unit some years later on my normally coil-ignitioned engine (2.7). I run them in tandem and don't need a tach adapter. On the other hand, I do need a resistor as the tach reads a little higher than normal.
Per Crane's tech line, some Porsche tachs are sensitive enough to pick up the signal; others aren't so sensitive, thus the need for a tach adapter (aka, transformer).
I guess this makes things a little muddier,
Sherwood Lee
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