I have a problem with my rev counter,on my w201 190 2.5 diesel.

I took out the cluster already to see if there's something wrong with the rev counter but I didn't notice anything,I bought a used one from internet to see if there is a fault in the tacho it self but it still don't work.
I changed the rev per minute sensor located at the bellhousing and still no signal.
I took the car to my electrician and told me the rpm sensor is ok,(is sending impulse).The problem is that the impulse is not reaching the tach.there is no impulse to the tacho.We checked all the fuses and they are all fine.
Is there a relay related with the tach?
Some thing that my electrician is suspecting is that the klima relay is not letting the impulse going to the tach,
Is that True?Does the Klima relay playing part with the tach?
Thanks

 

Any one?