where does the tach signal come from?

SON240sx Automotive
1

hey i have an s13 redtop sr20det, and i recently hooked up my safc 2 and was wondering where does the computer receive its signal from for the rpm, like i know its the 3rd wire on the pin out, to go to your tach but i am not receiving any signal from it at all, what can be the issue? can anybody figure this out?

thanks
chaz

2

Im not 100% positive but I’ve read that people go off the CAS for an RPM signal (example would be hooking up a monster 5’’ tach) so I would assume you could use the CAS signal but I could be wrong ?

So if I’m wrong, someone please correct me

3

so is this guy right about the cas being where my tach signal comes from???