The idea is taht since most of the electrical items in the car use the body as a ground point that the alternator grounds to the body. That way it does not depend on another ground wire to provide a return path for the electrical power.
One 4 gauge wire from the block where you connected the battery ground wire to
the chassis ground where the battery was mounted up front. Use a 5/16” bolt
and bolt down the 4 gauge engine to chassis ground, make sure that it the metal
around the bolt is clean & shiny. This is the alternator power ground.
