This is the plastic firewall plug.  Drill a 3/4" hole in it's center for the gauge wires.  Reinsert this plug.  Later, when all of your wires are run, you can reinsert the foam insulation piece.  Just cut a slit and a hole in it and insert it over the wires.  NOTE: If you purchased a complete DMI ISSPRO kit, follow the instructions that came with your kit for drilling this plug.  The Kit comes with 2 snap grommets that will be installed.