You will see not a square wave, not a sign wave but something in between is best I can describe it. Frequency will change with speed. Attach channel 2 to pin 25 and you should see a nice amplified clean square wave.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

Thank you I will try and post the results.

So, if I understood the route, signal, picking up at flywheel, goes straight to EDS, cleaning and amplifiyng there, then distributing to Klima and Tacho. Is that correct?
And one more moment: when I am disconnecting X62 connector, that leads straight to sensor, engine allmost stalling. That proves for me, at least EDS receiving engine speed signal and using it.

Yes the cleaned and ampilifed signal is also available on the diagonistic port just can't recall the pin number. Youtr logic of working is correct. Maybe try disconnecting the large connector on ECU clean and reseat that had fixed some problems for me in the past.

__________________
92 e300d2.5t
01 e320
05 cdi
85 chev c10

Yes, diagnostic port called X29/4. it's in PDF file I posted above. They say to measure a/c voltage over there. Mine was 3.6V that withing specs. But I still have some thoughts about tacho unit itself. As I mentioned above, it's had a blown resistor, i replaced it together with capasitor. Seems like the problem is well knowm. But... why it's blown???

I have never experienced a failure with an instrument cluster in a w124 so I can not comment.

__________________
92 e300d2.5t
01 e320
05 cdi
85 chev c10

Update. Week was so busy, was out of my home until Friday. Today got a chance to do some measurements with scope. I have good square wave with 8 V amplitude, not sure , but it looks like should be. Have exactly the same signal at ECM, testing connector X29/4 and at tacho input. That sounds for me, like my tacho unit is failed. Will attach photo of the scope screen. Sorry for quality. May be it will be helpfull for others.

Sorry, can't attach my picture, how I can do that? When I am clicking "insert image" button, it's asking me to enter URL of my picture. WTF?

Thanks everyone for response, my tacho is working now. In my case problem was blown 56 Ohm resistor in tacho unit(replaced it together with capacitor 100mcF 10V). Found that info at one of mercedes forums, don't remember exactly which one. And double check your fuses guys: I did it only when I just start my troubleshooting, fuse#5 in underhood box was good and tacho unit had power. But during my troubleshooting it blew up so even when I fixed tacho unit, it wasn't work. Replaced fuse and all is good. Still have no idea how to post picture of good signal waveform here, so it looks like allmost square with amplitude 8V. If someone still need it, please pm me.
Thanks for help again and good luck to everyone!