Tachometer goes crazy
 

Hello everyone, I have a '99 4x4 blazer, the tachometer needle has been failing for a while, it goes crazy sometimes, the rpm goes up to 5000-6000 and then goes down to zero, when it stays at high RPM it loses power, when it is at zero RPM it runs fine. It does it sometimes, especially when I activate the turn signals, sometimes when I activate them, all the indicator lights flash. What could be causing this?

I already changed the CKP twice just in case.

Is the behavior of the tachometer independent of how the engine runs or is there a correlation between what the speed of the engine and what the tachometer reads?