you can really put a ground anywhere.......there was one wire that was grounded under the carpet behind the seats in the trunk, i just grounded it there as well. i have a sedan, so idk if it would be different in a coupe. basicly you can ground to anywhere where theres a screw or bolt that touches metal and where the connector would touch metal......if youts painted, get some sand paper and sand down the paint to the metal, just where you need it, and that would be a good ground.