Fusible Link For Alternator - JeepForum.com
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post #1 of 33 Old 02-20-2021, 03:16 PM Thread Starter
Charleston82CJ7
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Fusible Link For Alternator

Looking at the POs wiring, isn’t there supposed to be a fusible link from the starter solenoid to the alternator? What is this?

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post #2 of 33 Old 02-20-2021, 05:56 PM
torkman1983
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That appears to be the main lead from the alternator that charges the battery. It goes on the same side as that red battery cable on the left side )cab side_ of the starter solenoid. Yes, there is a fusible link (just a special wire they used that would burn up like a fuse if there is a major short) that is normally in that line off of the starter solenoid. In my case, I eliminated the fusible link wire and instead added a large fuse that both the alternator wire and the main large red wire that goes to the main fuse box are both attached to.
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post #3 of 33 Old 02-20-2021, 08:44 PM
StoneTower
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If it goes to the alternator, it looks like someone used 2 smaller fusible links in parallel to protect the wiring from the alternator in case the internal regulator goes bad. Some people run the alternator charge wire to the starter relay that is mounted on the fender. It should go to the same side as the battery cable that comes from the battery if you do not run the charge wire directly to the battery.
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post #4 of 33 Old 02-20-2021, 08:50 PM Thread Starter
Charleston82CJ7
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Quote:
Originally Posted by StoneTower View Post
If it goes to the alternator, it looks like someone used 2 smaller fusible links in parallel to protect the wiring from the alternator in case the internal regulator goes bad.
Thanks, I was wondering if the two wires were some type of fusible link. That was all I could think they might be.
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post #5 of 33 Old 02-20-2021, 10:43 PM
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A potential problem with this is that you do not know if the previous owner chose the correct fusible links for your alternator amperage. It might be better to switch it out to a heavy gauge wire and a mega fuse.

One of these

https://www.amazon.com/Bussmann-HMEG...885847&sr=8-21

and a properly sized slow burn fuse for you maximum alternator output

https://www.amazon.com/Littelfuse-ME...00AOGM94&psc=1

I would use #4 gauge cable (I buy welding cable) and solder on some good quality copper terminals and you will have a first class setup for a fraction of the cost of one of the alternator wiring kits that are sold commercially.

https://www.amazon.com/Painless-3070...ustomerReviews

Quote:
Originally Posted by Charleston82CJ7 View Post
Thanks, I was wondering if the two wires were some type of fusible link. That was all I could think they might be.
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post #6 of 33 Old 02-20-2021, 11:01 PM
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I could be wrong, but, those look like standard wires of a smaller diameter.

Paperwork will ruin any military force.
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post #7 of 33 Old 02-20-2021, 11:08 PM
torkman1983
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Stonetower. Once he knows his alternator output, lets say it is stock at 63 Amps, what size Mega Fuse would you use? 80? 100?

Also shouldn't he have both the alternator and the main power to fuse box both connected to the same side of the Mega Fuse? If I remember right, in the stock setup there are Fusible Links (pink wires) on the ends of the main coming from the fuse box on firewall and coming from the alternator, both joining together at the starter solenoid. If so, seems he would get the Mega holder you linked and right fuse size (first question) and then just connect both of the reds (alternator and fuse box lines) to one end and the other to the battery side of the solenoid. Is that right?
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post #8 of 33 Old 02-21-2021, 08:41 AM Thread Starter
Charleston82CJ7
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Looking at the wiring diagram in the FSM, I should have a 10 gauge wire from the starter solenoid to the alternator, with a 14 gauge fusible link in line, right? I am guessing right now the battery is not protected if the voltage regulator goes out (unless the double wire is a fusible link). Also, I don’t see the other red wire that is supposed to go from the same stud on the solenoid to 12G on the fuse block. Does any one know what this is for?
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post #9 of 33 Old 02-21-2021, 08:47 AM Thread Starter
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Quote:
Originally Posted by StoneTower View Post
A potential problem with this is that you do not know if the previous owner chose the correct fusible links for your alternator amperage. It might be better to switch it out to a heavy gauge wire and a mega fuse.

One of these

http://www.amazon.com/Bussmann-HMEG-...885847&sr=8-21

and a properly sized slow burn fuse for you maximum alternator output

http://www.amazon.com/Littelfuse-MEG...00AOGM94&psc=1

I would use #4 gauge cable (I buy welding cable) and solder on some good quality copper terminals and you will have a first class setup for a fraction of the cost of one of the alternator wiring kits that are sold commercially.

http://www.amazon.com/Painless-30700...ustomerReviews

Quote:
Originally Posted by Charleston82CJ7 View Post
Thanks, I was wondering if the two wires were some type of fusible link. That was all I could think they might be.
So the factory wiring is grossly undersized.

How do you size the fuse for the alternator (looks like a stock Delco) 70 for a 60 amp output?
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post #10 of 33 Old 02-21-2021, 10:05 AM
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The general idea of that fuse is to protect the Jeep from a failed voltage regulator. A failed regulator can let the alternator produce 70 or 80 volts which is really bad for the wiring and all the accessories on a 12 volt system. It will burn out your gauges, radio, headlight and maybe even all your wiring in just a few seconds. The 4 gauge wire will be overkill for a 70 or 80 amp alternator but it is a cheap mod and has less resistance and it is future proof if you ever want to put in a larger alternator. You usually size the fuse to protect the wire that it is on but if the wire is oversized, you size it for what the circuit would normally need. If you have a huge cable, you do not want a huge fuse with a small load on the end of it will smoke the accessory before it will pop the fuse. I would choose a 100 amp slow blow fuse for this application. They use 150 or 175 amp fuses for Ford 3g (130 amp) installs. You want some headroom. If the regulator goes out it will pop a 100 amp fuse 70 amp alternator without a problem. You do not want the main battery lead on the same fuse. The starter or a winch can draw several hundred amps when they are loaded and hot and will pop the fuse. The alternator fuse protects the rest of the Jeep from the alternator.

So to answer the question about factory undersized wiring...the factory did things with economy in mind. Copper is expensive when you are making 100s of thousands of Jeeps. They did not expect all the bolt on lights and accessories that we put on our Jeeps. By AMC factory standards, the headlight circuit was just fine but those of us that have made a dedicated relay harness for the headlights know how much better and brighter the headlights are after the upgrade.

Another good practice in automotive wiring is to learn how to solder and shrink tube (marine shrink tube if you can as it has a heat activated sealant to keep the water out) all your connections. A Jeep that is used by its owner will see harsh environments and crimp connectors do not hold up well when they are repeatedly splashed with water and mud. A properly soldered and shrink tube sealed connection will outlast a crimp connection many times over. If you do it right the first time, you will not have to repair it later.
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post #11 of 33 Old 02-21-2021, 10:07 AM
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My "Mr. Jeep" is stock with the 14 gauge fusible link-----I changed to a 100 Amp alternator in 1989-----No issues at all. (You ain't seen any smoke 200 miles NW of you have you? Or heard a man Hysterically Crying over that a way?)

When I "Chicken Hatchery" wired up "Willy" from scratch using a '79 manual diagram for a guide restored '91-'93 .....I could not find a 14 at the parts store so I went with the next size up (back in 1991) I used a 16 gauge......I see now that Advance Auto Parts has the 14 and the 16 and others https://shop.advanceautoparts.com/we...fusible%20link

Posts 2-4 in this link https://www.jeepforum.com/forum/f8/l...et-up-4402453/

are diagrams I scanned from a manual and colored them in Microsoft Paint-----the "particulars" of why some things "Are" how I colored is up there in post 2. Makes things EZ to quickly trace out.

PM me if you want the originals scanned into "my pictures" , I'll send them, they are not fuzzy you might wanna make a big one like I did in last pic of post 2

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post #12 of 33 Old 02-21-2021, 10:30 AM
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This is a quote from a Mustang forum:

https://www.stangnet.com/mustang-for...erages.819889/

Fuse links come with a current rating just like fuses. A clue as to what current they are designed for is to look at the size wire they protect.

Choose the fuse according to the wire size.

Wire size current table:
18 gauge wire = 5-8 amps
16 gauge wire = 10-12 amps
14 gauge wire = 15-17 amps
12 gauge wire = 20-25 amps
10 gauge wire = 30-40 amps
8 gauge wire = 50-60 amps.

Fusible link colors
Link Gauge Color
20 Gauge Blue
18 Gauge Brown or Red
16 Gauge Black or Orange
14 Gauge Green
12 Gauge Gray

Keep in mind that the wire size in the chart is for the circuit itself, not the size of the fuse link. The packages of fuse link repair material you can get at the auto parts stores also will have a current rating on them."

By using this chart, you can see that a 12 or 14 gauge wire is never designed to carry anywhere near 70 amps. The alternator is only suppose to charge what the battery needs. If the battery needs 5 amps, the alternator is suppose to supply 5 amps. The problem comes in when you run the battery down and the battery need a big charge. This is when the wire can fail. You could have a 300 amp alternator with a 12 gauge charge wire if the battery is always fully charged and the voltage regulator is working properly. If you ran the battery down and push started or jumped the Jeep, you probably will melt down your charge wire.
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post #13 of 33 Old 02-21-2021, 12:32 PM
torkman1983
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Stone tower, makes sense. In the wiring diagram both the alternator and the main fuse feed line are both connected together at the starter solinoid and each have an in line fusible link but they come together with a single eye that connects to solinoid. So can those same two wires ( alternator and main fuse box lead) go to the 100 amp fuse together just as they did at the starter solinoid?
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post #14 of 33 Old 02-21-2021, 12:52 PM
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After thinking about it, the answer is no. If the alternator reg went bad, the fuse would blow to battery but keep feeding jeep fuse box which defeats the purpose. The fuse lead needs its own CB or fusible link.

Would an inline 30 amp fuse be enough for the main fuse box lead? He may be able to easily set up the above with his current wiring.
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post #15 of 33 Old 02-21-2021, 01:25 PM
StoneTower
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The fuses need to separate as you figured out to protect the individual circuits.

Back to the wire size. The wire going to the fuse box is (maybe an #10). You want a fuse to protect that wire. You may want a 40 amp mega-fuse or a 40 am maxi fuse. If you have a separate headlight harness, and do not have a big stereo you can go less. The smaller the fuse, the faster it will blow if there is a short or overload and the more protection you will have but if the wire regularly sees more than the rated amount, it will blow the fuse. If you have a circuit that will pull 10 or less amps max, you do not want a 30 amp fuse on that wire. The fuse protects the wire and the accessory.

Quote:
Originally Posted by torkman1983 View Post
After thinking about it, the answer is no. If the alternator reg went bad, the fuse would blow to battery but keep feeding jeep fuse box which defeats the purpose. The fuse lead needs its own CB or fusible link.

Would an inline 30 amp fuse be enough for the main fuse box lead? He may be able to easily set up the above with his current wiring.
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