The alternator will fry itself in short order and at around 105A output, it'll spark, but not be too problematic. The battery can and most often will start a fire if it shorts to ground with a heavy wire. Can it happen with stock wiring, sure can. Stock wiring most often has a harder wire coating than most aftermarket stereo wiring kits though.

Where I have seen engine fires with aftermarket equipment has not been due to a collision, but due to either faulty wiring or fasteners backing off. In one case just 2 months ago, a fairly knowledgeable person lost his car because of a power wire to the alternator. He was able to put the fire out with a fire extinguisher before we (the fire department) got there, but the damage to the engine compartment was already done. Cause, the fastener on the alternator power wire had backed off and the wire arced to ground igniting some oil in the engine compartment near a fuel line. Real cause, the self locking nut that was used on the alternator output stud was not engaged into the locking feature due to the large aftermarket connector used on the wire.

If you want to see how much of an arc a battery will produce, take a battery that can be destroyed and dead short it. I recommend having some fairly long wires and use proper protective wear. Do not short it for long as the battery can explode with prolonged contact between the leads. We did this very thing for an vehicle extrication course I took a few weeks ago to show us what can happen.

Do it or don't it really is personal preference, but to say it is pointless is a bit excessive. If it were pointless, then there would not be fuses on anything. Nor would practically all Big 3 how-to's mention a fuse on this wire.

 

No offense meant, and not to jump on a band wagon, but do vehicle manufacturers do everything perfect the first time? If they did would you be upgrading the big 3 in the first place? Just because they decided to cut corners to save costs doesn't mean you shouldn't put in a fuse to protect your investment. You've already invested a lot of money into your truck, so why not spend a couple extra dollars and fuse that alternator wire?

 

I'm prolly more aware of how batteries spark than 90% of people with over 3 years selling and refurbing electric forklift batteries (12v-68v was the biggest I played with).

Like I said do whatever helps you sleep it night. I really could care less if you run 2 fuses in the alt-battery wire cause thats what it is gonna take to kill both ends if there happens to be a short and no big 3 upgrade mentions this.

As for the wire insulation, I don't use the pretty, overpriced stuff from stereo shops. I have industrial welding cables with wire sleeve on mine. It aint as flexiable or as pretty but short of running it in 3/4 inch EMT its not going anywhere. And running under the truck to the amp in the rear it is in 3/4 EMT.

 

Good for you on the welding cable. Its damn good stuff. My jumper cables are made from it. That is not what 95% of the people that do this run though.

And I just did a quick google search for "Big 3 Upgrade" and out of the first 5 "how-to's", 4 of them mention fusing the alternator wire, but it looks like 3 of them are reposts on various forums (which is the same thing that Jon posted here).

 

Cause damn near every one is nothing but a repost or just reworded so they can take credit for it. I first heard about the upgrade a while back in stereo forums and it has since trickled down to almost every auto related forums.

If your gonna suggest a fuse for protection you just as well suggest one on each end. I don't know about any of you but most guys that do this have also upgraded the battery and alternator to bigger ones. Both of which will create a bigger and hotter spark than the smaller factory installed counterparts.

I still say its pointless to add a fuse.

 

i've had my big 3 for 2 years now,and had it in my s-10 for 5 years...never fused the hot wire,never had any trouble...just my $00.02

Damon