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Tach Signal Coming out of RPM


TomSSS

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I'm trying to find out which wire out of the PCM is the signal to the tach. I'm in the process of developing some electronics and it would be helpfull if someone who knew which wire out of the PCM is the signal going to the tach could fill me in. That way I don't have to tap into all wires or tear my dash apart to find the signal.

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Well if anyone is interested the tach signal is the white wire coming out of the wire harness attached to the gauge cluster.... At least that's what it is on my SS

 

 

Some info:

 

The tach signal at the gauge appears as if its a 4 cylinder, so you need to convert it. At the PCM it's as if the polarity is switched (you don't get the same signal from the PCM that you get from inside the cab). I don't recall the plug and pin number at the PCM (it is still a white wire -- want to say pin 57 but really dont remember).

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if it helps anyone any, i used the white wire in the main harness underneath the fuse box to tap in for my magnavolt. there are two wires that are white in that harness, i knew which one it was because my remote starter was tapped into already.

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Well if anyone is interested the tach signal is the white wire coming out of the wire harness attached to the gauge cluster.... At least that's what it is on my SS

 

 

Some info:

 

The tach signal at the gauge appears as if its a 4 cylinder, so you need to convert it. At the PCM it's as if the polarity is switched (you don't get the same signal from the PCM that you get from inside the cab). I don't recall the plug and pin number at the PCM (it is still a white wire -- want to say pin 57 but really dont remember).

 

 

That's correct. 4cyl at the gauge cluster.

 

If anyone is interested in this....signal to the tachometer has a frequency proportional to the actual RPMs. For 8cyl engines you would take frequency*15 to get actual RPMs. For 4cyl engines I believe it is frequency*30.

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