It IS an actual plug ripped from a 5ME MA61 loom. It's the connector between the 5ME dash harness and the 5ME ecu harness.
This was done to make it a plugin affair for a 5ME MA61. If your's doesn't have this plug, then i would just cut the connector off (on the ECU side of the connector) leaving it in the car and splice into the existing plug harness.
ie. just use the existing plug you have in your car.
Depending on how you wire it up, you will probably only need to wire up temp gauge and tacho...assuming you have the digital dash.
I have about 30 wires in that harness that im not using, we had to cut off the plugs to make it fit through the firewall anyway. Most of the wires were for gauges, ABS, and a bunch of other features our cars don't have.