you should ground your car with the fattest awg wire size you can. i have my big 3 done with 1/0 awg wire. i plan on switching it out later with 4/0 awg welding wire when i do a bigger sound setup. if you are running a stock alternator than 4ga awg wire or 2ga awg wire is fine, but if you upgrade to a H/O alternator, 1/0 awg or larger is recommended by most companies(Mechman, Irragi, DC)