when i first got my car the head unit would lose sound randomly. upon furthur investigation it appears that our cars dont have a ground wire in the harness. the head unit is supposed to ground through the chassis, (theres a metal bracket behind it that it rests against). if it's not touching that it's not grounding. i followed the ground wire leading out from my head unit and found that it just ends at the other end of the harness, so what i did was take that ground wire and screw it into something on the chassis. you can get pretty creative, i chose the metal shift boot

. little sanding to give it good clean contact and then just screw it in. you dont have to do it here, u just need to find a part of the chassis to use as a good ground.