What is the 'Negative' terminal post connected to?

[FcukThis]

Proceeding with upgrading the Big 3.. in my Sedan
Even though I doubt it'll make a dramatic difference with this tiny alternator Toyota has given us..

In previous attempts, grounding completely new wires omitting the original stock negative terminals turned out inefficient. In such cases, the car did not start. I received power (Lights,Radio..etc..) just fine, however that was about it. There is nothing wrong with the grounding points i have selected either; they have been tested.

Anyways.. Does anybody know exactly what the Negative Terminal post is linked to ? By this i mean the negative grounding points toyota has provided.(the one you connect to your negative battery post)

It seems that there are two wires in which the terminal splits into. One directly visible on the chassis and second one that slips underneath the battery-mount...I can't seem to trace it. Just wondering if anyone knew.