Where does this wire belong?

The only wiring that I know of behind the grill and in front of the radiator is the Outside Temperature Sensor.
This should be the sensor that displays the Outside Temperature in the Climate Control display screen. Are you missing this temperature readout?

If this is the wire it would not make any difference in the way the car drives and would not trigger any warning lights that I am aware of. The Climate Control System uses this sensor in the fuzzy logic to control cabin temperature. I also believe that the HV battery cooling fan control uses this sensor.

There is a plastic cover over the top of the radiator in the engine compartment. If you remove this plastic cover you should be able to see this sensor in front of the radiator and the wiring going to this sensor. It looks like you should be able to splice the wires back together with a butt splice.

 

From the pic, it looks more like a black pipe cleaner that was used to attach something to the front grille. Maybe a bow or red Rudolf nose at Christmas.

 

Do you have a higher quality picture? It doesn't look like the bundle of wires that run to the outside temp sensor, there are to many of them.

 

it's probably the hood latch wire.

 

+1

 

It may have been to hold something to block the grill during winter.