It should have this internally already, enabled when aux 4 is used as the tach output.
I’ve found with older tachometers that are designed to pickup off the coil negative, Black and Classic need an adapter. I haven’t measured it personally but supposedly the negative of the coil field collapsing can push voltages well beyond 12 or 14v (I’ve read 60, not sure about that tho), some tach’s (Toyota’s for example) there’s an inline resistor you can bypass and then Aux 4 does the job.