Ok i have searched...checked tested and cameup wid some good results regarding BIG 3
Before i should begin how to do big 3 .....it is necessary for me to explain what is big 3 so here it is
First Read the post then ask any question u want ! specially gforce 
It is not necessary to upgrade this thing ...it is a good modification regarding the electrical system of a vehicle.Sometimes i c dimming head lights on high volumes .It means vehicle voltage is droping below 12Volts.It can be dangerous for ur amp as well .Big 3 is a group of three wires which consist of
1) wire from alternator to battery positive
2) Battery negative to chassis
3) Chassis to engine
donot replace the stock wires i repeat donot replace them ...just add some another wires so that the current finds the pathway of least resistance wire automatically.thats y we are adding a thicker gauge wire to the system hence the term is used "UPGRADE"
Now i suppose i must also tell what basically each wire do :S
Think of ur car charging system as two different systems first one is the battery and amplifer and the other consisting of your alternator and your battery.The current in your electrical system flows from your positive battery terminal to your amp, from your amp's ground to the chassis, and then from the chassis back to the negative battery terminal. But how does it get to the positive terminal in the first place? That's where the alternator comes in. Current in the second circuit flows from your alternator's positive post to the battery's positive terminal, then from the battery's negative terminal to the chassis, and from the chassis back to the block, which happens to be the grounding point for your alternator.So the positive wire from the battery u connect it wid + of the amp and ground of the amp to the chassis (seat ya diggi).From here the current needs a way to get back to the negative battery terminal, and that way is through the first of the "Big 3," the battery negative to chassis wire. Upgrading this wire will "upgrade" the circuit between your battery and your amp by giving the current a larger path to flow through to get back to the battery.
Now the wire btw alternator to battery positive is the second step.The alternator to battery positive wire supplying "power" to your battery. From there the battery, just like your amp, is grounded to the chassis through the wire mentioned in the previous paragraph. Again, the current needs a way to get from the chassis back to the alternator's "negative terminal" and that way is through the last of the "Big 3," the chassis to engine wire. Since your alternator is most likely mounted to your engine block using a metal or conductive mounting bracket, you can simply add your new wire from the chassis to one of the mounting posts for the alternator. Upgrading these two wires will "upgrade" the circuit between your alternator and your battery, again giving the current a larger path to flow through.
Comming up next wid some pictures the whole process
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