Well... The early Z's (1970-1973) take a different approach than the 1974-1978 (and later) models. The early's "sense' the current flow to the coil. The power supply to the coil from the ignition switch is looped at the back of the tach and the tach is probably sensing the amp flow.
The lates "count" the number of times the coil fires and derive an PRM value from that. They get the pulse signal that causes the coil to fire from the electronic ignition.
At any rate, they are wired completely differently. I don't know if the stock wiring is going to work once you've swapped in an EFI engine. Perhaps, if you've kept the power to the coil "pure" (wired exactly as stock and with no additional components on that wiring...) but I'm not sure. I've never had that problem since I have a 260Z. My tach however has worked with all different kinds of electronic ignition modules over the years...
edit: forgot to mention that there are tach adapters made to allow old, original tachometers to work with more modern ignition systems.
1974 "early" 260Z - L28ET - F31 ECU, MAF, Coil, TPS - FMIC - T04E .63 A/R - 400cc Injectors, MTX-L Wideband - NIStune! - 5-speed - Coilovers - Big Brake Kit up front, lowered just enough... Sakura Garage - Tempe, AZ
Last edited by cgsheen; 04-17-2017 at 07:37 PM.