The speedo works, no so the tacho

I got the speedo working today. It has an optocoupler to interface the frequency output from the VFD to the 12 volt active low of the speedo. See images below.

I cant for the life of me get the tacho going. From checking the wiring when I removed the ignition, there is a 1k resistor from the low (switched) side of the coil to the tacho. I have tried a high side opto and low side but no success yet. I really want the taco going so I can use it to read out RPM, torque, current, voltage or whatever parameter I choose.