(I couldn't help myself, I sent a message to the Ebayer (Gene) who makes that signal amp, including a schematic of the Veglia tach-- he replied that they hadn't tested one themselves, but their interpretation of the connectors (esp, noting a "-" and "+" pin suggested that it was a current-triggered amp--when in fact, the signals are Battery (+), the middle post is ground, and the final pin is the signal (and if I remember correctly, Fiat 850/124 tachs don't have the post connector and maybe sequence differently, but the same circuit board is used on everything no matter 4 or 8 cylinder or for a Harley). For real geeks, the proof of a voltage triggered tach is the C4 cap in front of the Q1 transistor...
for just $8 shipping to New Zealand, maybe you can be the one who can confirm to Gene that it really works 
I have some time coming up (Chinese New Year just 2 weeks away) and I'd love to pull my pieces from the closet and test myself...!
