What controls the Tachometer?
 

I have a 2001 chevy blazer. 2wd. The tachometer started going crazy. Its being followed by a clear ignition or fuel injection problem. The computer codes show that it is either the Cam sensor or the Crank sensor. I figure that the one that directly controls the Tachometer is the one that needs to be replaced.
Thanks

Neither has direct control. They send signals to the powertrain control module and that sends a tach signal to an I/C in your dash cluster. It's mainly the crank sensor (I think). BUT if the crank sensor is screwing up you'd also notice your engine running oddly. No crank sensor signal means no fuel delivery. If it's running good but tach is messed up I'd go with a cam sensor first. Running bad like the fuel system is kicking on & off replace the crank sensor.