Thread: Alternator Fusible Link(s)

I managed to create a short at the alternator. A bit of smoke and a pop came from abouts the region of where the alternator wire gets to the starter, and the rest of the electrical system on the car seems fine, so I am relatively certain that the damage is confined to the alternator section of the circuit. I think I blew at least one of the three fusible links.

First, where do the smaller red wires off of the starter go? Second, once a fusible link blows, it is gone for good, correct? On to diagnosing, I ran at it with my multi-meter. The battery is definitely not charging. I am getting very slight voltage at the alternator wire post on the alternator. Shouldn't I be getting something there? Does this allude to both the alternator and the wire being bad, because if the alternator worked it would be creating voltage, and if the wire was good, I would be reading voltage from the battery? Any suggestions on where I can get a replacement alternator wire?

If the alt is not getting any feed voltage, it cannot make any voltage, I may seem weird, but it takes some electricity for the alt. to produce


If you need, get a cheap positive batt cable from a local parts store, and run it from positive terminal on batt to positive stud on alt, If it charges after this, than alt is still working

Edit- Make sure above wire is clear of the belt

Awesome news, thanks guys. I have parts to replace the fusible links, so keep your fingers crossed for me that I did not kill the alternator!

After looking the circuit over better, I realized how poor the stock alternator wiring is. The wire is at least ten feet long, and looks to be 12gauge wiring. It runs down to the starter, then has to work back to the battery from there. Instead of all of that nonsense, I simply did the "alternator rewire" from the alternator to the fuse box. I used an inline maxi-fuse and a short length of 4gauge wire, so now the smallest wire in the system is 4gauge. I cut out what I could of the stock alternator wire, then capped it off. All is well again, and probably better than before.

This brings up a good point about the alternator rewire, though. Running a wire from the alternator to the fuse box without a fusible link or fuse leads a direct path to the battery and the rest of the electrical system. Had that been the case when I created the short, things would have been a lot uglier. The fusible links are there for a reason, so if the alternator were to fail the same problems could occur. My point is, the alternator rewire done without inline protection creates potential for serious electrical gremlins!

That is a good point. But the best one could do I imagine would be to install a fusible link again (4 wire gauge sizes smaller, and would see to defeat the purpose of the alternator rewire to a degree) or some type of inline fuse able to handle the current, but the only place I could think of getting such a thing would be from an audiophile shop or something like that and even then I dont know if they would have them big enough to handle full load of the alternator.

It would almost seem more sensible to put in a automatically resetting circuit breaker or something like that.

Originally Posted by SyntheticShield

That is a good point. But the best one could do I imagine would be to install a fusible link again (4 wire gauge sizes smaller, and would see to defeat the purpose of the alternator rewire to a degree) or some type of inline fuse able to handle the current, but the only place I could think of getting such a thing would be from an audiophile shop or something like that and even then I dont know if they would have them big enough to handle full load of the alternator.

It would almost seem more sensible to put in a automatically resetting circuit breaker or something like that.

If you can get a circuit breaker, that is great. I just use a maxi-fuse, although I will most likely find a fusible link when I get the time. The alternator is rated at 110A, so a 125A maxi-fuse should suffice:
Fuse, 125 amp, 32 VDC, Mega Fuse
You can find them at parts stores. Mine is actually a higher amperage, again do to availability at the time. This is the same setup I have run on another car, along with many other folks, with no issues. The fuse has always done its job.

To be fair, the absolute correct way to do it would be with another fusible link. Fusible links are "better" at protecting the circuit overall, without the potential for blowing under instantaneous spikes like fuses or circuit breakers. I would recommend something like this:
* Fusible Link

My opinion is that the best option is to include the listed fusible link with the alternator rewire, then remove the stock wiring from the circuit. I know that everyone says to leave the stock wiring connected, but that is going to be harder on the system...just like running two 8ga. wires in parallel is not the same as running one 4ga. wire!

You can go to the battery section of the parts store and find an assortment of length 4ga. wire that has eyelets on both ends. I went with the shortest I could find, because I made the routing as direct as possible, as at the time I was not considering rewiring the alternator. It cost me $5, then another $5 for the maxi-fuse. It is not tucked away as neatly as the alternator rewire "mod" but it is functional. My 2¢.

Originally Posted by JoshMcMadMac

If you can get a circuit breaker, that is great. I just use a maxi-fuse, although I will most likely find a fusible link when I get the time. The alternator is rated at 110A, so a 125A maxi-fuse should suffice:
Fuse, 125 amp, 32 VDC, Mega Fuse
You can find them at parts stores. Mine is actually a higher amperage, again do to availability at the time. This is the same setup I have run on another car, along with many other folks, with no issues. The fuse has always done its job.

Well I guess I stand corrected. I dont know why I thought they would not make fuses in that high of a rating for automotive applications. Thank you for that find piece of information.

Originally Posted by JoshMcMadMac

I know that everyone says to leave the stock wiring connected, but that is going to be harder on the system...just like running two 8ga. wires in parallel is not the same as running one 4ga. wire!

FINALLY!!! Someone that gets it. Ive got my harness completely out of the car and I intend on fishing that sucker out of there (the stock alternator wire) and I have, from day 1 of installing the alternator re-wire, left the OEM unconnected and taped up.

You are just chock full of good info, keep up the good work and thank you for sharing.

Originally Posted by JoshMcMadMac

I know that everyone says to leave the stock wiring connected, but that is going to be harder on the system...just like running two 8ga. wires in parallel is not the same as running one 4ga. wire!

True, but running a 4ga and a 8ga is better than just a 4ga. The reason being that current travels on the surfaces of metal conductors and one 4ga has more surface area than two 8ga. A 4ga plus a 8ga has the most surface area of all. Simple laws of parallel circuits. Besides, electricity will take the path of least resistance which will be the new wire. The old wire being there or not doesn't change anything as long as your new wire stays the same gauge and length. I deal with issues like this all the time when re-wiring the B-52H ECM systems.

Originally Posted by SyntheticShield

FINALLY!!! Someone that gets it.

I don't want to sound harsh, but his perception is a little misled. Comparing adding the rewire to changing out two 8ga with a single 4ga is apples to oranges.

Compare a 4ga to an 8ga with a 4ga. That's what the alternator rewire does, and you will see lower overall circuit resistance with the combined setup. Parallel circuits at work.

This is actually the basis of your whole car's electrical system (and any electrical system). Closing a circuit (headlights for example) is just adding a parallel circuit to what was already on (your fuel pump for instance). The overall system as a whole now has a lower resistance (more parallel paths to take) and that results in more current. Current = load.

Voila.

Sabrewings, good info. I made the example of two 8ga. wires, as it is easier to do the math than a 4ga. and a 12ga. Regardless, like you said you are cutting resistance and in turn increasing current...which is good, to a point. However, I am not interested in trying my luck with what could or might (or not) occur when that long, relatively thin stock wire starts taking on more current than designed from the factory. It is already underrated for its duty, and I feel much more comfortable not taking the chance that it would take a dump. There is nothing to be gained from running a short 4ga. and that long 12ga. IMO, yet there is potential to cause issues. For me, that makes the decision simple.

Originally Posted by SyntheticShield

FINALLY!!! Someone that gets it. Ive got my harness completely out of the car and I intend on fishing that sucker out of there (the stock alternator wire) and I have, from day 1 of installing the alternator re-wire, left the OEM unconnected and taped up.

Fishing it out is not the word for it. Be prepared to disassemble the wiring to get it out. There is electrical tape around the wires, then the wire loom is taped over that! If it is out of the car it should not be too difficult, just be prepared to remove and replace a fair amount of tape.

Oh yeah. Ive already determined that GM could cut the cost of a vehicle significantly by using less electrical tape.

I figured I could post a final update. First and foremost, the mega fuses are designed for alternator use. So, no need to worry about fusible links. I picked up a short 4ga. wire from the auto store and a mega fuse. For the time I just bolted the mega fuse to the alternator, then the wire to the mega fuse, planning on ordering a fuse holder within a few days since the only place I could find them was online. Apparently the alternator is subjected to a lot more heat than I would have thought! The fuse ended up getting so hot that it started to melt, causing an intermittent fault. So, the fuse definitely needs to be mounted on a holder. After looking around online I discovered that I cannot get a mega fuse and a holder for less than $20, and that is before shipping. As much as it is a proper solution, I decided to yet again check the parts store for an alternative. They had a 150A circuit breaker for $28, so I went ahead and did that instead. For basically the same price as a mega-fuse setup I have a unit that I can reset, and I had it done that day instead of waiting for parts to come in the mail. This also makes it easier if I ever need to pull the alternator...I can just open the breaker!
Stinger SCB150 Car Audio High Current Multi Use 150 Amp Circuit Breaker

Moral of the story:
If I were to do it from scratch, I would go to AutoZone and get a circuit breaker and three of their 2ga. pre-built battery wires, since the 2ga. wires are almost the same price as the 4ga. Just choose the shortest lengths possible to route where you mount the breaker. Run one wire from the alternator to the circuit breaker. I mounted mine on the firewall. Run the second wire from the circuit breaker to the fuse box. Run the third wire in place of the factory wire from the fuse box to the battery. My opinion is that although it is more like $40-$50 instead of the $20 "alt. rewire" out there, it is the right way to do things.

Thank you for posting that sir. I think this needs to either be stickied or put in the How To section with a list of parts you used and your directions. Very good info. Thank you for taking the time to do this.

Originally Posted by JoshMcMadMac

Stinger SCB150 Car Audio High Current Multi Use 150 Amp Circuit Breaker

Moral of the story:
If I were to do it from scratch, I would go to AutoZone and get a circuit breaker and three of their 2ga. pre-built battery wires, since the 2ga. wires are almost the same price as the 4ga. Just choose the shortest lengths possible to route where you mount the breaker. Run one wire from the alternator to the circuit breaker. I mounted mine on the firewall. Run the second wire from the circuit breaker to the fuse box. Run the third wire in place of the factory wire from the fuse box to the battery. My opinion is that although it is more like $40-$50 instead of the $20 "alt. rewire" out there, it is the right way to do things.

Ok so let me get this right? For your "big 3" rewire. You are using ONLY the new 2ga line from the Alternator to the "fuse/breaker" and then another 2ga wire off the fuse/breaker to the Battery? And do you then totally disconnect the Factory Alt wire from the Alternator? And then do you do the other two alt grounds, ie one off the Alternator bracket to the the Strut Tower and then another one from the Battery to the chassis?

Just trying to figure this out.

Originally Posted by GeddyLee

You are using ONLY the new 2ga line from the Alternator to the "fuse/breaker" and then another 2ga wire off the fuse/breaker to the Battery?

That is what I would recommend. I went 4ga., but after looking at the parts section in AutoZone you can go 2ga. for just a few bucks more...it makes sense to me.

Originally Posted by GeddyLee

And do you then totally disconnect the Factory Alt wire from the Alternator?

True.

Originally Posted by GeddyLee

And then do you do the other two alt grounds, ie one off the Alternator bracket to the the Strut Tower and then another one from the Battery to the chassis?

I have not touched the grounding, although I am sure I can look into it.