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Hello all, Looking to hear from someone who has done the big 3 upgrade on a 2009 duramax. I have a couple questions. I have done big 3 upgrades on a few other vehicles which had alot less going on under the hood making it all a no brainer. Now being that this truck has 2 batteries and 2 alternators im just curious if big 3 turns into big 6 lol. Do each battery need to have - to block as well as + to each alternator? As well as block to chassis? Im not looking to cut any corners I want it done right im just not sure if your supposed to do each battery and each alternator or if one is fine being that it is in paralell. I have searched everything I can find online and theres very little info. I know theres also a voltage regulator that is supposed to be on top of the ground wires that tells the alternator when and how much to charge (apparently a gm thing). I do not see this unit on the drive side near the battery like I seen online. Is it possible this truck does not have one or mayby I was looking at an older model online. Also I read from one user not to do any positive leads due to to many amps travelling through the path of least resistance and possibly frying some cables? Never heard of something like this before. Ive read to leave all oem cables in place and just do a second run. Anyone that has done big 3 on a duramax please lemme know how you did yours and if you have had any issues... Thanks for reading!
 

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2008 GMC Sierra crew cab 4x4 LMM
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Hey Dirty,

Did you ever end up finishing this project? What did you learn? Can you share about your project and what you learned, if you did do this? I am wanting to do the same on my 08 LMM. The only difference is I only have one alternator.
 

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2008 GMC Sierra crew cab 4x4 LMM
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If anyone has done this, I’d like to know how much length of cable was used for a truck with both batteries done and one alternator. I’m also aware that the lengths of wire used on each battery needs to be the same length. So that’s one thing to consider from what I read & understand when doing this.
 

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Each battery grounds independently to the block, so that's an extra ground for one of the batteries. I doubt that same length cables will ever be noticeable, probably not even measurable in the ever changing conditions of a running, driving truck. Clean, tight connections are the key. Volt drop all your system now, then after you complete your upgrade. Let us know how it turns out.
 

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Sub'd... and waiting........
 

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Gents... FYI, the OP hasn't been logged into the forum since Dec. 2020...
 

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Alright I'll pour a drink and get comfy...
The anticipation is killing me.....


But honestly. After learning about the voltage regulator. I couldn't see it when I poked my head over the fender while wiring in some BusBars for my winch install. Made me think maybe there's an issue there as to why my batterys don't last long at all probly ony 6th or 7th set on a 15 year old truck that's ridiculous.
 

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Even though OP has disappeared - lets keep this thread alive. I Used to do big 3s when i was doing sound systems. It really is a great setup, not sure why he hasn't become an OEM thing.

Dual batteries with dual alternator - i would say just run each side independent. One alternator to one battery and the other across to the other side. Although, i do strongly agree any system should be load tested to really know what you need.
 
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