Got the adapter plug for the car and it has a black wire for the ground. The ground coming off the plug for the headunit has a metal circle attatched to it to bolt to the chassis. Do I cut off the metal circle and solder it to the black wire on the plug or do I tape off the wire from the adapter plug and ground it to the chassis?

If grounding it to the chassis where is the prefered spot?

 

Either, it doesn't matter. I cut off the ring and used my factory ground.