amp wiring, firewall on a 96 aurora

i would like to know what is the best way to find the firewall on a 96 aurora. my last car i was able to run my 4 gauge wire through a hole i found but my aurora doesnt have that same setup. what would be the proper way to do this and also someone told me that i should run my ground wire to my battery, is there any truth behind that. it seems like that would supply to much  to the amp

Running the ground back tto the battery is not the best way to do a ground on an amp it should be a short distance from the amp usally about 2 feet at the most. As for there being to much power by running it direct to battery (this would not happen the voltage should be the same as long as the proper gauge wire was used)

Mobileoys is correct, you want to keep your ground short from the amp to the chassis. However, depending on your application it is not a bad idea to run what is called a "return ground" from your battery to your amp in addition to your chassis ground. This will help eliminate potential noise problems and only needs to be a thin gauge wire(16-12awg). As far as running your power wire into the cab, there is no easy spot that I aware of on an Aurora, but see if you can find a grommet with wires going through it that is readily accessible on both sides. If you can, carefully use a razor blade and cut the grommet away from the existing wires in an X and run your wire through your X and then be sure to seal the hole with silicone. If the grommet idea looks hopeless on that car which I seem to remeber being the case you can drill a hole thru the firewall but be careful doing so and maybe even seek someone professional to do it for you if you don't have experience doing this as the potential for error can get very expensive. good luck