my earth for my amp is the bolt for the seat belts under the back seat thats the best place for it but try not to make the earth more than 12inches long ,but then its only the best place to earth it if your putting the amp on the back of the back seat or on the floor near the back seat but if you were thinking of puttin it on one of the sides use the bolt that holds the seat belt roller fingy under the shelf suports hope wot i said makes some sense.ian