I have an Autometer tach and no longer use the stock tach. Ive been trying to figure out how to get a signal to it. I found this thread on AEM How to wire/setup your Autometer Tach with AEM

Can someone confirm this is the correct way for the EMS 4 as well? thanks

 

Yes, you need a pull-up resistor for the tach signal. I should of wired that in for you, but didn't even think about it. I like to use this type of resistor. Much more robust than the regular ceramic resistors you would get at Radio Shack.

RH0252K200FC02 Vishay/Dale | Mouser

http://www.mouser.com/images/vishay/images/rhnh.jpg

 

yes same as EMS-4. I'm using a 2.4k resistor on mine.

 

You need a 500ohm resistor or you can just use a small light bulb