Tachometer testing

Thread Starter


Joined Mar 20, 2020
So bare with me guys n gals, I'm a mechanical engineer that occasionally plays with electronics.

Let me explain what it is I am doing/what I am attempting to accomplish. So I am attempting to bench test the tachometer for a 1969 Gto, it just came back from the builder who "made" it compatible with electronic ignition systems (very reputable company). Now, most people would simply install it and assume all will be fine. Not me... I need to see it work infront of me on the bench before I spend the time installing the tachometer and removing it if it does not work correctly (entire dashboard removal).

So now that I have explained what I am doing, let me explain what I have done thus far. So i am aware that my ignition system is going to produced a 12v square wave at 50-1000Hz. So i have a cheap sunpro tachometer that i use for testing (https://www.summitracing.com/parts/sun-cp7903) and a cheap amazon signal generator to produce a squarewave signal (https://www.amazon.com/KKmoon-Frequ...734926&s=industrial&sprefix=signal+ge,aps,173). With the sunpro I attach the positive and negative leads to a small 12v battery, then the positive signal lead from the generator to the signal lead and the negative lead from the generator to the negative power lead from the tachometer.

Now when i do this same procedure with the gto tachometer i get nothing, not until i move the 12v lead from the aux. power source to the output of the signal generator does it work, but that procedure does not seem correct to me.

So the conclusion I have come to, is that i need a single powersource on the gto tachometer, and the cheap generator does not have a 12v dc output. and if that is what i need to test this accuratly can someone point me in the correct direction of where to obtain this!


Joined Nov 18, 2012
The majority of tachometers from that era that I remember only needed battery positive, ground and a sine wave signal to make them work. They were pretty much all that way if I recall. If a 4th wire was added, it was for illumination

DNA Robotics

Joined Jun 13, 2014
With your electronic ignition, does it still have one coil? If so, get the tach signal from the negative terminal on the coil.

If not, intercept the tach signal from your new system and use battery voltage with the engine running.