So I bought a sub and amp a while ago and installed them myself. But at night my lights dim if I turn the boost on. So I need to do what is called "the big 3". Basically its upgrading the wires under the hood and I need their locations.

I have a 2012 Mazda 3
Heres what needs to be upgraded.
Battery to chassis (this one is easy..)
Battery positive to alternator positive (I need to know where to run this wire, I know where to hook it up, where would be safe to place the wire?)
Engine ground to chassis (where is the engine ground on Mazda3?)

Heres the guide I was given by multiple audio experts:
http://caraudioforum.com/showthread.php?t=339865

 

just run power for the amp directly to the battery... both wires, don't use the chassis for ground.
If it still dims you probably need a capacitor @ the amp.
what kind of power are you running & what size fuses are you using from the battery & @ the amp?


To answer your questions:
you can probably fish a larger wire along side the existing harness to the alternator, split loom tubing was used on portions of the wiring & covered with tape, other sections just tape covered.
Engine ground is on the battery side of the engine as I recall, it's an obvious wire once plastic is removed. There's another ground to the engine / frame under the 3rd engine mount too (upper passenger side of the engine)