the tach on my 72 240z just doesnt work. the guy who owned it before me had put in a 280zx 5-speed and electronic ignition, i think it has something to do with the transmission. unfortunately, the previous owner was not very thorough in some of his work and decided not to fix the problem. he said it was something about a resistor or some other crap, but it looks like there is a tach output from the distributor cap that isnt connected to anything whatsoever. i dont really need the tach, i just would like to have it working.