Upgrading Big 3

Hi there, Im new to the forums but i was wondering if anyone could direct me exactly to a few wires for upgrading the big 3 under the hood for my car audio. I have a 1992 Buick LeSabre. The battery Negative (-) to ground is easy to find. The Positive (+) battery terminal to alternator i can also find. What i want to know is where the engine block to ground is? Is this wire easy to locate? is it under the alternator? i just want to be sure. Maybe someone has done the big 3 for this car. Any help would be great.