ok. well I just put that 8awg wire between my alt. and battery and Ive noticed pretty good difference in how much less voltage drop Im getting.Right now I have
1.extra 8awg between alt and battery (small red box)
2.a 4awg wire ran from my battery ground to a random body ground nearby
3.and my amp's 4awg wired straight to the red box
number 2 might sound a little off but Im pretty sure it helped even if only a lil bit.
with all of this, Ive noticed a not huge but a very good difference compared to how it was before any of that extra wiring. Definitely dont feel like I need a big battery like the one they wanted to sell me. but Im not sure what to do yet b/c I still gotta put the other amp in there with my high's and see how much that draws from everything.
If I were you, I would run 4awg from the battery + straight to the alt, bypassing the red box. The red box contains a fusible link and is there for safety. Also run your amp wire (with the appropriate fuse) straight to the battery +. This should help with your dimming issues.