# where does the tach signal come from?

**URL:** <https://forums.speedlife.net/t/where-does-the-tach-signal-come-from/109217>\
**Category:** SON240sx Automotive\
**Created:** [September 6, 2007, 5:28pm UTC](https://forums.speedlife.net/t/where-does-the-tach-signal-come-from/109217 "2007-09-06T17:28:15Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Two4Tchaz](https://avatars.discourse-cdn.com/v4/letter/t/9fc348/32.png) [@Two4Tchaz](https://forums.speedlife.net/u/Two4Tchaz)\
**Post date:** [September 6, 2007, 5:28pm UTC](https://forums.speedlife.net/t/where-does-the-tach-signal-come-from/109217/1 "2007-09-06T17:28:15Z")

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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

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**Author:** ![Jedi\_Car\_Fan](https://avatars.discourse-cdn.com/v4/letter/j/b9e5f3/32.png) [@Jedi\_Car\_Fan](https://forums.speedlife.net/u/Jedi_Car_Fan)\
**Post date:** [September 7, 2007, 6:37am UTC](https://forums.speedlife.net/t/where-does-the-tach-signal-come-from/109217/2 "2007-09-07T06:37:59Z")

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> [@I need to learn how to drive](https://forums.speedlife.net/t/i-need-to-learn-how-to-drive/13949/53):
>
> 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

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

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**Author:** ![Two4Tchaz](https://avatars.discourse-cdn.com/v4/letter/t/9fc348/32.png) [@Two4Tchaz](https://forums.speedlife.net/u/Two4Tchaz)\
**Post date:** [September 12, 2007, 3:50pm UTC](https://forums.speedlife.net/t/where-does-the-tach-signal-come-from/109217/3 "2007-09-12T15:50:05Z")

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