The easiest to do it is tap it directly from your conversion harness. Otherwise, you will have to add pins on the stock side harness then route the wiring to these:

*VTEC solenoid
*VTEC oil pressure sensor +
*VTEC oil pressure sensor -

If GSR head, run these additional pins/wires:
*Secondary butterfly +
*Secondary butterfly -

If you have an OBD2a (96-98 civic), I have a conversion harness for sale. If you buy it, I'll help you tap the wire. $100......