RPM Gauge not working, noticed alt not putting out, replaced it with new, notice in new alt box said, if you have a dodge cummins and rpm is not showing, the problem is tack sensor, ok WHERE IS TACK SENSOR ?? storm coming, Thanks

 

It's called the engine speed sensor (ESS) and is located at the dampener (lower pulley at the engine front). Follow the wires down to it. In fact your sensor could be fine, problem could be damaged wires or the sensor's connector near the top/front of the engine could be dirty. Also check the gap between the dampener and sensor, it should be about the size of a folded in half business card.