# MK5 Jetta Big 3 Upgrade



## Blkzilla (Jul 24, 2008)

This post was taken from AsymmetricalDichotomy's Audio Build. here



John Reid said:


> *If you guys replace the alt cable* (the stock cable on my '09 MKV JSW was 4 gauge, surprisingly), you'll need to get specific lugs for it to bolt on, at least on the alt side of the wiring.
> 
> You'll need 90 degree bend lugs; I got mine here.
> 
> ...


John
Is your JSW and 2.5L or 2.0T? Do you have a diagram of the engine electronic system? 

My Jetta is a 2.5L.

I read in this thread on sounddomain that replacing the existing cabling is just extra work. I supposed that aesthetically it would look better but its not necessary b/c current takes the path of least resistance. Replacing any of the existing cabling is not necessary.

Is this the boot your talking about needing to remove in order to replace the battery to alternator cable?









There are two cables from the battery's positive. One leads to the fuse box next to the battery and the other connects at the point circled in the pic below. I think this is the connection that connects the alternator and battery positive but I'm not 100% that this is the actual positive terminal of the alternator. I just want to be sure about what Im doing before I get this part of my project started.










If anyone has done a big 3 upgrade on an MK5 w/ 2.5L please chime in. Thanks!


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## thygreyt (Jun 7, 2009)

i might have... lol..

http://forums.vwvortex.com/showthread.php?5420607-THY-GREYT-s-audio-build-thread

but tell me, what are the big 3?


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## Blkzilla (Jul 24, 2008)

The big 3 improves the current capacity of three cables that are part of electrical system of the car. This upgrade effectively lowers the overall resistance and provides benefits like:

1) Reduced dimming and smaller voltage drops
2) More stable voltage and better current flow
3) Less strain on your vehicle's charging system

The Big 3 are

1) Battery negative to chassis
2) Alternator to battery positive
3) Chassis to engine


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## AsymmetricalDichotomy (Aug 13, 2010)

Sub'd! :beer:


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## John Reid (Jun 30, 2010)

****ing post died on me. Have to rewrite.

Yup, I have a 2.5L. And yup, that's the infamous boot.

The circle you show is the 4 gauge cable that I replaced with aftermarket, and that cable also needs a 90 degree lug for it to work (you can see the stock lug the image you posted). 

I also replaced the second cable with aftermarket 8 gauge. IIRC, both cables ultimately run to the engine bay fuse box.

For the battery ground, I used the stock location, but ground off the paint before I bolted the new cable on.

My MKV JSW has a 140 amp alt, so technically I could probably have gotten away with leaving all the wire stock, _but_:

1) I'm used to upgrading the Big 3, from when I used to compete (you lose points if you don't do it)
2) I have a 1950 watt system in the JSW, so given that the stock wiring is designed to work with a stock load and not much else, I felt it would be worth it.
3) I'm a bit anal retentive when it comes to my car audio installs.

All car audio will be hotly debated, since it's such a subjective thing, and SoundDomain _can_ be a hotbed of misinformation, so always take what you read there with a grain of salt. 

Personally, I'd say that if you have, I dunno, a 500 watt stereo system, upgrading the Big 3 would be worth the effort. It *won't* be a night & day difference, but it won't hurt, either.

Old pics of the battery area in my car. In the first image, there are 2 wires coming out of the plastic battery container. One is fused (main battery power), the other wire to the right is the upgraded alt cable... I just routed it differently than stock to clean things up a bit. If you follow the cable line with your eye you'll see it exit the battery box on the right side and terminate in the main fuse box.


















I'll try to get a pic of the alternator area, but I think you have a good grasp on it.

Anal Retentive Chef FTW










By the way, there are a few members that frequent this section that'll probably have better info than I do, since they install for a living. NFrazier is one of them, another is (I think) [email protected] or something like that.


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## Blkzilla (Jul 24, 2008)

Im running 2000 watts.

What size fuse is that on the main power line?

Did you ground the alternator to the chassis?

Do you have any dimming? My dim enough for me to notice and that toooo much for me.


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