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.

 

Do you happen to have a picture of that set up???

 

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.

 

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.

 

I could be wrong, but, those look like standard wires of a smaller diameter.

 

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?

 

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?

 

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.

 

Charleston82CJ7

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/w...b/SearchResults?storeId=10151&catalogId=10051&langId=-1&searchTerm=fusible link

Posts 2-4 in this link https://www.jeepforum.com/forum/f8/lights-main-power-wire-hei-set-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

-----JEEPFELLER

 

This is a quote from a Mustang forum:

https://www.stangnet.com/mustang-fo...stang-forums/threads/advice-on-fusible-link-to-maxi-fuse-what-amperages.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.

 

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?

 

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.

 

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.

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.

 

With respect to everyone you may be getting confused between fuses and fusible links and how they were used by AMC.

The fuses are sized to the equipment on the end of the line. a problem with the equipment will cause the fuse to blow.

The fusible link is harness protection, they do not blow like fuses. They are sized to the wire!!!!! This is your last defence against harness and Jeep meltdown from a short of the wire. They rarely blow. When you buy one you size it to the wire you are installing it in. They are also quite cheap.

It is the case that Maxi fuses are now used where fusible links used to be but they have different performance characteristics than fusible links. Fusible links continue to be used in most starting circuit applications.

And most people installing larger alternators will never see significantly more amperage along those wires. A larger alternator generally has more capacity lower down the speed range which will keep the charging circuit up to its required level more easily when crawling, (a significant benefit, apart from requiring more cooling fan which absorbs engine power)but the power requirements of the Jeep are unchanged. Even with a "200 Amp" special you will rarely see more than 40 Amps in a CJ.

Using welding cable to connect the alternator and solenoid is not great when you then have a 14 gauge fusible link. You could leave it out but......

 

The reason the factory used fusible links is because they are cheap and easy to install. Today, like lots of other electric things, time electrical components are cheaper and better. Fuses are now readably available that are slow blow and that is duplicates what a fusible link does. A slow blow fuse or a fusible link can handle a over amperage load for a given period of time. A fast acting fuse will pop when the rated amperage is reached. Companies like Painless Wiring do not use fusible links, they use the proper fuse for the application. Fuses are now relatively cheap and if you have a spare, they are easy to replace in the field.

With respect to everyone you may be getting confused between fuses and fusible links and how they were used by AMC.

The fuses are sized to the equipment on the end of the line. a problem with the equipment will cause the fuse to blow.

The fusible link is harness protection, they do not blow like fuses. They are sized to the wire!!!!! This is your last defence against harness and Jeep meltdown from a short of the wire. They rarely blow. When you buy one you size it to the wire you are installing it in. They are also quite cheap.

It is the case that Maxi fuses are now used where fusible links used to be but they have different performance characteristics than fusible links. Fusible links continue to be used in most starting circuit applications.

And most people installing larger alternators will never see significantly more amperage along those wires. A larger alternator generally has more capacity lower down the speed range which will keep the charging circuit up to its required level more easily when crawling, (a significant benefit, apart from requiring more cooling fan which absorbs engine power)but the power requirements of the Jeep are unchanged. Even with a "200 Amp" special you will rarely see more than 40 Amps in a CJ.

Using welding cable to connect the alternator and solenoid is not great when you then have a 14 gauge fusible link. You could leave it out but......

 

Interesting that if you go to the Painless web page and look at their instructions for where and how to place their included Mega/Maxi fuse (100 amp) in the Jeep harness, they say to put BOTH the alternator and the main wire to fuse box together on one side and battery on the other. As discussed earlier, I think that is wrong.

If internal alternator goes bad and sends high amps down line, the breaker will blow to stop sending power to battery. But, since red to fuse box is tied together with alternator, that same surge of power will go directly to the fuse box even after fuse blows. This is not how the stock system worked.

In the stock system, even though both the fuse box main and alternator terminate together into a single connection at the starter solenoid, they each have their own independent fusible link. If alternator surges too high, it’s fusible link will melt and stop the alternator from sending any power to the battery or the fuse box. In that case, alternator is completely isolated from the system.

Can someone explain why Painless says to connect the harness that way? How is the main fuse box protected in this set up?

 

I don't know why either because if the alternator was to die, short out or something and blow the fuse. Then your jeep would die also. Lights also. Kinda scary in the dark.
You could of made it safely if you had two fuses. As the jeep would run off the battery. You could run a reasonable time on just the battery. At the least, get you safely off the road.

A lot of people don't realize this but up until the CJ's had computers, there was no fuse for the ignition circuit. Even then, the fuse only protected the computer, the the ICM or coil. The lights are protected by a self resetting circuit breaker. Some years even had a Circuit breaker for the vipers.

Besides your harness will melt down a long time before a 100 Amp fuse will blow.

For example Littlefuses Midi fuses ratings

time to open a 125 amp rating running at:

• 75% or 94 amps --------unlimited
• 100% or 125 amps -----unlimited
• 110% or 137.5 amps ---unlimited
• 150% or 187.5 amps---3,000 seconds
• 200% or 250 amps-----100 seconds
• 300% or 375 amps ---- 3 seconds
• 500% or 625 amps ---- 1 second

 

I guess I'm always looked at as the "Grinch" when it comes to changing CJ stuff that has worked well for many years.

I can maybe understand some of this if one chooses to drag race, use it as a submarine, run heavy/ industrial accessories, or want to energize a portable KISS concert stage.

I'm not Mr. Statistical, I'm guessing the other 99% of us rarely have an issue other than corrosion, or a wire or ground having shook loose over the years.

To add to that, whether it was you or another soul, here's the abnormal stuff the other 99% deal with: Self inflicted shorts (blown fuses), MIS-Wired components, Additional wiring (indiscriminately tied in), Missing parts or wiring. Some of this is "Adopted" along with their acquiring their Jeep from the dark side.

Where I am going with this is when your Jeep is predominantly back to normal.....(Sorry, I'm one of the guys that either had one Brand new CJ or one a couple of years there after---Back when they were mostly un-monkeyed with).

We have few problems electrically...........Myself, The biggest problem that has happened quite a few times over the years is Mr. Starter continuing to revolutionize Mr. Crankshaft after you turn loose of the key!

There are a few possible reasons this could happen (mostly self-inflicted), But the common and sorta non-preventable reason is the SOLENOID is internally stuck together. (periodic replacement could help).

Soooooo, it runs and runs....Big cable wires get RED HOT (I've never had a fire) The insulation melts.....The STARTER gets really HOT (Damaged???...Probably a shorter life)......Unless you have a cutter or a wrench YOU ARE HELPLESS!

I'm sure others of you have done what I did..........after the 3rd or more time......Install a Heavy Duty switch between the battery and the solenoid.

FOR THIS REASON AND OTHER ELECTRICAL MALFUNCTIONS---THIS SHOULD BE A #1 FIX FOR THE NEW JEEP GUY!

Other electrical teachings might include tying lights and other accessories off of the battery, installing dedicated fuses and the several ways a relay can be wired to A) Turn on Bigger Wires B) Only allow items to be energized when, for instance, when the key is turned on.......thus leaving the onboard, already wire sized and fused stuff alone!

If this practice had been in use way back, much of the screwed up wiring would not be present today!

That was really my only Whines about the normally driven CJ electrics.

----JEEPFELLER

 

As noted above, fusible links are color-coded. I went to the U-Pull-It lot and snipped off a few of every color I could find. They didn't even bother to charge me for them. So, I not only got the right one for my upgraded alternator, but now I'm prepared for future needs, and for free.

 

Maybe to finalize for the OP, you need one wire from Alt to battery with either a fusible link or a fuse/CB. You need a separate wire that runs over to your fuse box on drivers side. Check out any number of wiring diagrams to see which wire it is. If your Jeep and dash have power, there is a feed from your battery...find that feed and use either a fusible link or Fuse/CB to protect your harness. That’s pretty much it.

I do think we can get a bit carried away with fuses, CB, extra switches, relays, etc. Much like Jeepfeller suggests, these things have run across deserts, mountains, mud, snow, high water, by the 10s of thousands with nothing more than the stock wiring. Very few have ever had a fire or anything more than a blown fuse. There are some bad examples I’m sure, but stock these Jeep’s have taken pretty much everything thrown at them.

Good luck! Great thread!

 

Another thing to think about is age of the wiring harness. As a harness ages, contacts and connectors become dirty and corroded and resistance goes up. Insulation becomes brittle and wears through. I would argue that fuses are even more important in a vintage vehicle than they are in a brand new vehicle.

These Jeeps were inexpensive new. Saving a few cents is very important to companies trying to compete with other manufactures. If you have an all stock Jeep and are happy with the way it works, good for you. If you are changing and upgrading your Jeep, you might as well use good wiring practices.

 

I don't know if this is what you want or not.

Someone else might modify my diagrams to show you what they mean!

This is just part of (the left side) a 1979 Diagram that I scanned and colored

I just went back and Deleted much of the surrounding stuff so it might be EZer to read

For the full 1979 Diagrams (left and right sides) and explanations on why I colored them this way.

See posts 2-3-4 in this link https://www.jeepforum.com/forum/f8/lights-main-power-wire-hei-set-up-4402453/

-----JEEPFELLER

 

I'm sure there has to be some guidelines in the racing world as far as safety and electrical wiring go.
i know one thing was the battery cutoff has to be mounted on the outside of the car. And a couple of times i wished i already had a battery cutoff switch.
There might be many more. Anyone know? It's been decades since I looked in a SCCA rule book.

 

Just be smart about it, do not do what this guy did

https://indianauto.com/stories/man-sets-his-jeep-on-fire-for-viral-tik-tok-video-nid3185

 

That reminds me, I need to get a new fire extinguisher.....

 

I need to check mine as well. Although pricey, I'd like to get one of these and mount under the hood. Like the idea of a self-releasing extinguisher, and one without all the dust. There are a couple interesting (and compelling) youtube videos demonstrating how these work.

Hoov

 

Halon ??

 

14 gauge fusible link in place from solenoid to alternator.I found the missing 10 gauge wire that goes to the fusebox. PO wired it to the alternator. Another fusible link installed and its back on the solenoid where it belongs.

 

I thought I would share my experience with an alternator issue that was intermittent over the last 2 years. After replacing alternator, new belt, sense wire, etc the alternator still wouldn’t charge. the intermittency got shorter and shorter until it stopped all together. I was pulling out my hair on this until I stumbled on this thread.

this morning I traced the wire from the alternator to the solenoid, it was enclosed in that plastic spiral covering, and original. When I came to the place where the fusible link was crimped to the wire, Saw that not only had it sort of disentegrated, but in 2 pieces.

off the the auto parts store, 14guage fusible link wire, with 12 guage red plus copper crimps. it Now works perfectly.