since you already have an aftermarket HU in there, it will already be connected with a wiring harness... you can either re-use it (less optimal), or just put out the $7 for a new one (optimal)... then it's just color coded from there
Just took a look at the harness, it looks like a black plug with wires coming out connected to the factory wires, then the harness from the head unit is crimped with those wires coming from the black plug. I hope that made sense lol.
That's what it should be. When you buy a new head unit, it comes with the harness that plugs into the back of the unit and has wires that would go to where you see the crimps. The harness you need for your car is the one that goes from the crimps to the factory harness. I would just cut the wires on the harness you need for your car right beside the crimps. Then you can just strip the wires and reuse the harness for your new unit.