To quote you quoting faria ...
Connects in series with the ignition switch so coil current flows thru tach.
Implies this is for a gas engine, detecting pulses from the ignition coil....
So you'll need several amp fast pulses to drive it ... there's probably an internal small pulse transformer to extract this. And yes eg a 555 could in principle provide this. And an arduino better, with a muich larger frequency range
I've got confused over the thread - is this for a vehicle? if so does it have an old fashioned contact breaker/ coil type ignition?
there's a way to simulate this in hardware otherwise ..... but are the sense wires you're connecting to totally isolated from all other connections? - to confirm my guess of an internal pulse transformer?
regards
Allan