I've read about different grounding locations for the HU and wanted to know if there is one preferred over the rest.
1.Black wire in factory loom
2.metal in dash
3.Running ground wire to rear batt neg.
or any other suggestions.

 

if your just installing a deck then the ground in the factory harness is fine. but if your adding a 4 channel mids amp then its a good idea to run the HU ground to the back to prevent ground loop

 

Thanks Emperor. I will have a 4ch amp so looks like I will run the ground to the back batt.

 

yup i would run it directly into the ground input for the amplifier. that way they are getting as close to the same "ground" as possible