I believe you tap the ground of an ignition coil for most rpm gauges.

 

Aftermarket gauges look for a pulse every cylinder firing, so that trick doesn't work any more with COP ignition. Most computers still direct drive the tach -as opposed to a CAN message. If that's not available, you can buy a module that converts your 1 pulse from a COP to 8 pulses.

 

Alright gotcha. I was just going off memory of hooking one up A couple years back on a project and I figured all the coils grounded to the same point so it would still read the pulses. I would pull the schematic for the PCM your running and see if you can track down where it sends the signal to the cluster.

 

Tttt