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Discussion Starter · #1 ·
[This is for a 2003 Frontier Crew Cab 4x4]

OK, so I didn't INTEND this to be an investigation, I was going to upgrade the wiring between my alternator and battery today but I ran into some confusion and wanted to talk it through.

I have a new alternator that makes 115A, and it says I need to upgrade the alternator to battery cable to 4 gauge.

What it took me a while to understand was that despite that terminology, there's really not a cable that goes straight from the alternator to the battery :)

Here's what I sorted out. It appears that all of the wiring coming off the alternator comes up this wire loom and out near the air filter box. The two white wires are power coming off the alternator, the black one is a ground to the body and the 3 colored wires are the control wires or whatever you call them.

The two white wires enter a loom that snakes from the driver side fender across the front of the truck and over to the fuse block.



The two white wires are connected to one side of the 120A fuse in the middle of the fuse block.



On the other side of the fuse is a red/black wire, looks to be around 8 gauge.



The red/black cable comes out under the fuse block and runs to the positive terminal of the battery.



Here's another shot of that wire (it's the one with the green trim near the top). The big ugly flat terminal lays under the similar one on the battery-to-starter cable and they get screwed down to the battery terminal.



OK, now to talk through what to do.

Clearly I could run a 4 gauge wire from the alternator and let it follow the wire loom across the front and over to the battery area.

When I looked at charts to see how large a fuse I needed for 4 gauge I thought 120A sounded right, so I bought a fuse holder and a 120A fuse I was going to put inline on the new cable.

But if the fuse block is set up with its own 120A fuse, can I just run my 4 gauge cable to where the 2 white wires connect on that fuse now?

And on the down side of that same 120A fuse in the fuse block I could upgrade that black/red cable to 4 gauge as well.

Am I missing anything?

Do the 2 white wires go anywhere else that I need to worry about?

Do I need a second, higher amp fuse before the cable gets to the fuse box?

Is 120A too little? Will a 115A alternator "spike" occasionally and blow the 120A fuse?

Note that I haven't added a new stereo or anything that would increase the demand for power, I was just stupid and thought a bigger alternator might not have to work as hard, not knowing I was going big enough to get into 4 gauge territory.

Thanks,
-Jeff
 

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2003 Nissan Frontier Specifications

Not sure what your truck is but this says that the SE model has 100A Alternator over the 80A alternator in the XE.

I never dug into the alternator wiring and setup so I don't know if your fuse will be the right size. One way to check is to find the alternator fuse that you have now and the alternator AMP size you have now and compare.

You defiantly want to get this right else your truck could turn into a big ball of flames.

I'd also check the FSM and see how the system works now.
 

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Discussion Starter · #3 ·
2003 Nissan Frontier Specifications

Not sure what your truck is but this says that the SE model has 100A Alternator over the 80A alternator in the XE.
It's the SE and according to the FSM the 120A fuse means it has the "heavy duty electrical system".

So I'm only jumping from a 100A alternator to a 115A. I feel a little better about that.

-Jeff
 

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It's the SE and according to the FSM the 120A fuse means it has the "heavy duty electrical system".

So I'm only jumping from a 100A alternator to a 115A. I feel a little better about that.

-Jeff

Does the FSM say that the SE has the 100A alternator? Reason I ask is that I have not read all of the FSM and the link that I gave to you may or may not be accurate.

The SE model has some small enhancements like Limited Slip and I believe the alarm package. Also the 2003 & 2004 have upgraded brakes as well. So there are a lot of slight differences in all of these years and makes and the FSM doesn't always specify the changes. (especially the brake enhancements).
 

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Discussion Starter · #5 ·
Does the FSM say that the SE has the 100A alternator? Reason I ask is that I have not read all of the FSM and the link that I gave to you may or may not be accurate.
Here's what the FSM says about the alternator, and it doesn't distinguish between models:

Nominal rating 12V - 100A

Hot output current (When 13.5 volts are applied)
More than 24A/1,300 rpm
More than 71A/2,500 rpm
More than 98A/5,000 rpm
 

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on my 02 xterra, i ran a 1/0 wire directly from the output bolt on the back of the alternator, through a fuse, to the positive battery terminal. i left all the factory wiring in place.

i apologize if i have over simplified what seems to be a very complex task.
 

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on my 02 xterra, i ran a 1/0 wire directly from the output bolt on the back of the alternator, through a fuse, to the positive battery terminal. i left all the factory wiring in place.

i apologize if i have over simplified what seems to be a very complex task.
:laugh:


jeff i dont understand why you dont just leave it alone? what damage is it gunna do?
 

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what damage is it gunna do?
there is potential for a very large fire, which is why you have to use the proper sized wire, and the proper sized fuse.

Jeff, to answer some of your other questions, a 120a fuse should be sufficient. the alternator might be rated at 110a, but it is regulated to put out exactly what is needed to keep the vehicle running and the battery charged. so if you arent running any high demand accessories, there is a good chance that alternator will never decide it needs to put out 110a. the max fuse size should be determined by the size of the wire and its length. there are charts available to see what category you fall into.

the fuse is there not to keep the alternator from sending too much juice to the battery, but vice versa. the fuses job is to keep the batterys juice isolated from the vehicle. in the event of a front end collision, many times wires can get pinched in the carnage. if the batteries(or alternators) main line is pinched it would be a dead short and the battery would then discharge as much of its energy as it could into the vehicles sheet metal. with the fuse in place, it will pop before any major damage can occur.

as far as hooking the alternator up to the fusebox, by all means if you want to waste time and effort. the fusebox is connected directly to the battery using a few feet of wire. so hooking to one is the same as hooking to the other. you will find however the battery is much simpler to access and more willing to accept a 4ga wire.
 

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Discussion Starter · #9 ·
OK, then I'll leave all of the factory wiring attached to the alternator PLUS run the 4gauge I have from the alternator, through a fuse and to the positive terminal on the battery.

If the concern is the line getting pinched, should I place the fuse holder close to the battery end?

I did think I had read somewhere here that the fuse also protected the system from the alternator throwing a big spike on failure but with both paths fused I guess that's OK.

I have a 120A ANL fuse for the inline. I might could go higher but I'm going to start with that for now. If neither that nor the one in the fuse block gets blown I'll be more comfortable that the alternator isn't sending in too much current.

So I'm back to Plan A, really. There are definitely 2 camps - those that say to do this, and others who don't have a better idea.

( Well, other than trying to return this alternator and going smaller, but we're way past that! :) )

Thanks,
-Jeff
 

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So you didnt change the 120amp fuse in the fuse box? I only ask because I am now upgrading my altenator in my 4cylinder Frontier. Stock it has a tiny 70 amp alt. The factory fuse is an 80amp. I am upgrading to a 270 amp alt for my stereo system. The wires from the alt to the fuse box seem ridiculously tiny....even for a 70 amp alt. I am upgrading the wire from the alt, both pos and neg to 1/0, with a 300 amp inline fuse from the pos wire to battery connection. I decided to upgrade the wires to the fuse box as well....both from the one under the hood to the fuse box inside as well.
on my 02 xterra, i ran a 1/0 wire directly from the output bolt on the back of the alternator, through a fuse, to the positive battery terminal. i left all the factory wiring in place.

i apologize if i have over simplified what seems to be a very complex task.
 

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the fuse for the fuse box is for the fuse box. it was not for my massive stereo. therefore, it did not need to be changed. my massive stereo had its own fuse connected directly to the battery. and my alternators output to the battery was also fused.
 

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Lol, thanks for the response Scott. Yeah I know that fuse is just for the fuse box under the hood as well as the fuse box next to the driver's side under the dash. I was just wondering if anyone upgraded this. Sorry I left out more information that would have explained why I asked. I have added several additional electronic devices via the interior fuse box thus creating more of a power draw. My Frontier is a base XE model with no essentials. No power locks, no power windows, and instead of a 120amp fuse for the fuse box, I have an 80 fuse. Because of the added electronics thru the fuse box, I upgraded to the 120 amp fuse. Sorry for making this longer than necessary. Appreciate the expertise however. :)
the fuse for the fuse box is for the fuse box. it was not for my massive stereo. therefore, it did not need to be changed. my massive stereo had its own fuse connected directly to the battery. and my alternators output to the battery was also fused.
 

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on my 02 xterra, i ran a 1/0 wire directly from the output bolt on the back of the alternator, through a fuse, to the positive battery terminal. i left all the factory wiring in place.

i apologize if i have over simplified what seems to be a very complex task.
This is the same thing I'm going to do on my 2008 Nissan Pathfinder S 4.0L V-6. I only got the wire that runs from the battery to the alternator left, this is part of the BIG 3 UPGRADE I'm doing to the Pathfinder in order to be able get as much voltage as possible into my starter battery. I just hooked up a second battery in the rear of the vehicle to operate my aftermarket stereo system. I also hooked up a NVX SMART ISOLATOR to try and stop one battery from draining the other! I've got 2 questions, first question should the red led light on the isolator stay on all the time, and 2nd question is does my 2008 Pathfinder have a smart alternator on it?
 
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