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2G Where does a 2g ECU get the Tach signal from?

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Well, Just to give a little back ground. I deleted the ignitor and the wires coming from it. In doing so I didn't realize the Tach signal was Incorporated in those wires. I am using a AEM and Msd box. I wasn't getting any signal to the tach.

What I did was took the original wire coming from pin 58 and connected it to the original wire (white connector under radio) (i believe its pin 8) o to the tach. This is the way it is run in the original harness from Mitsubishi. And, what do you know, the tach is working correctly.
 
Just to confirm, doing the same thing as Kenne, I am running an AEM with ARC2 box and no ignitor, and redoing the entire harness.

Do I simply need to run the pin 58 to the white connector under radio, or do I need to splice in the ARC2 tach signal to this connection to utilize the stock dash tach?
 
Just to confirm, doing the same thing as Kenne, I am running an AEM with ARC2 box and no ignitor, and redoing the entire harness.

Do I simply need to run the pin 58 to the white connector under radio, or do I need to splice in the ARC2 tach signal to this connection to utilize the stock dash tach?
To utilize the stock dash tach just run the wire from pin 58 to white connector, not the arc.
 
Perfect, thank you!

The ARC2 tach signal would be utilized if I want a secondary tach (i.e. aftermarket tach setup), correct?
 
You could use it for that. Keep in mind a couple of things though. Your signal from the AEM may work smoother in some cases.

If you are on a launch limit or top end rev limit, dropping sparks in the AEM box, then your CDI ignition(ARC-2, MSD, whatever) won't see any input signal pulse. So it won't put out a tach pulse either. As a result, your aftermarket tach might bounce around more on the limiter. And if you are trying to run any other devices like RPM window switches off that signal, they might become erratic too.

Ideally, the AEM should be able to still put out a smooth tach pulse on the rev limit, since it is the one reading the cam/crank sensors.
 
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