im in my garadge with a buddy finished my amp and specker install but i had the amp grouded to under the 3rd brake light in the trunck but after i raise the volume it toggles from power to protect so idk i had it attached to a metal plate in the trunk but it was the fuel pump cover and wasn't sitting on the trunks metal it was sitting close to it on 3 rubber feet so yea idk where was anyone else grounded to that worked