that blue wire COULD be coming from the alternator, he's showing a shock tower mount. Which does kinda look like a distributor plug, if that's what you were thinking.

Wiring diagram for OBD1 teg, that blue wire would be "alternator output signal"

do with the info what you will.

Tach signal, sounds reasonable to me. Is the VX like the DX no tach in the gauge cluster? That would explain it...

-PHiZ