Jeep CJ wiring - JeepForum.com
 
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post #1 of 6 Old 06-23-2021, 12:47 PM Thread Starter
Oostivan
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Jeep CJ wiring

Hi all
So I am busy re wiring my whole engine compartment and I have run into a few problems.
So first off Iíve replaced all the 16 gauge wires with 14 gauge wires, is that ok?
Then I replaced the 10 or 12 gauge alternator wire with a 8 gauge. Originally it had a 14 gauge fusible link connected to the alternator wire. Can I use a 14 gauge resistor wire on the 8 gauge wire as I cannot find any bigger resistor wires?
Then there is a small brown wire ďthink it is 20 gaugeĒ also connected to the alternator running directly to the firewall fuse box. From my understanding it is also a resistor wire. So my question is if it is running directly to the fuse box why does it have to be a resistor wire? If so can I replace it with a bit bigger gauge resistor wire as I donít have such small ones? Hard to find these where I am from.
Thanks in advance.
Oh by the way it is a 1979 cj7 6 cylinder.

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post #2 of 6 Old 06-23-2021, 11:46 PM
BagusJeep
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All those wire choices sound fine.

The fusible link is usually 2 sizes smaller than the wire next to it, it is harness protection so is quite independent of the fuse box. For an 8 gauge this would be a 12 gauge link. 14 gauge is fine, it will certainly stop your wires from melting. If you are running the same size alternator, it will never fuse anyway.

As to brown wires, it depends on how your CJ is wired. It sounds like the exciter wire that goes to the Field terminal and is fed by the ignition circuits. On some vehicles it is wired through a warning light on the instrument panel which is about 15 Ohms. When you do not have a warning light, you need to drop the voltage to a specified level so they put in a resistance wire.

This is a PITA to reproduce so I suggest you get an industrial 50 Watt 15 Ohm power resistor and just use 16 gauge wire and feed the resistor from the ignition circuits. Check your local electronics supplier and they will have one. get one with a nice finned heat dissipation case that you can screw on to the bulkhead and run your wire through that. About $5 from a good shop.

Or use any resistance wire in a larger gauge as long as it is 15 Ohms.

BagusJeep lives in Bali with far too many 4x4s:
1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
1995 Cherokee 4.0 - CHEROKEE
1980 Land Rover Series III 109" troop carrier - ROVER
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post #3 of 6 Old 06-24-2021, 04:29 AM
John Strenk
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I agree, I think the 14 ga fusable link would be fine for protection.

If you have the duraspark ignition, there is a resistor wire there also. It can be replaced with a solid wire and a ballast resistor.
I think it's 1.3 ohms but I'm not sure.

Bagus is spot on about the alternator wire. the 79 should be hooked up to the ignition system.
The resistance is different for a 4 cylinder for some reason. but you have the 6 cylinder so you should be OK.


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post #4 of 6 Old 06-24-2021, 09:24 AM Thread Starter
Oostivan
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Thanks for the info guys! I should be done soon with the harness. Just waiting on a delivery so I can finish the last few bits. Iím also replacing the pigtails with Deutsch connectors, they look quite good and tidy.
Just one last question. Will it be ok to replace original fusible links with bigger gauge fusible links?
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post #5 of 6 Old 06-25-2021, 02:07 AM
BagusJeep
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Fusible links are harness protection.

They are there to stop your harness melting under load. The first thing that melts is the fusible link which is in a flameproof sleeve, so no harm and no engine bay fire.

If you put in a larger fusible link, there is a danger the harness will melt, the Jeep will go up in flames etc. Hence you must match it to the cable being protected, the actual size, or smaller. As you are making the cables larger you can go for a larger fusible link in some areas but it must be 2 AWG sizes smaller.


- The largest current draw is the starter motor but this cable has no fusible link. It has a key and solenoid so if it starts to smoke, you let go of the key, no fusible link needed.

- Second largest is the battery charging by the alternator, which is the large cable from alternator to solenoid. This has a fusible link. You can size this to the cable you use. Stock was a 10AWG cable, 14 AWG fusible link.

- Third largest is the solenoid to fuse box, stock is 10AWG wire and 14AWG fusible link. This has a fusible link which you can size to the cable used up to the fuse box and light switch. If it passes through the bulkhead connector, make sure you have sized it to the smallest cable either side. Unless you have completely replaced the wiring, this is likely somewhere to be the original size cables. So put in the original size fusible link!!!

- Fourth largest is the headlights. For safety they have no fuse but they do share the fusible link with the fuse box feed. They instead have a momentary circuit breaker within the light switch, so your headlights do not go out at night just for a 5c fuse.

The amount of current you will ever see in a stock CJ, except when using the starter motor, is less than 40 Amperes as that is the real capacity of a CJ alternator. The larger cables you are installing will reduce current losses but will not significantly impact the current flowing unless you increase the demands by putting in more electrical gear AND increase the size of the alternator.

A healthy CJ wiring system needs grounds as good as the positive wiring system and relays to avoid relying on 40 year old switches in high current systems such as the headlights. these are worthwhile modifications to make.

BagusJeep lives in Bali with far too many 4x4s:
1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
1995 Cherokee 4.0 - CHEROKEE
1980 Land Rover Series III 109" troop carrier - ROVER
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post #6 of 6 Old 06-25-2021, 02:16 AM
BagusJeep
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And here is a gratuitous shot of a man setting fire to his Jeep with gasoline. He may just as well have deleted the fusible link!!!
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BagusJeep lives in Bali with far too many 4x4s:
1981 CJ7 258ci - Bagusjeep
1984 CJ7 258ci - Puthijeep
1981 J20 258ci - Gladys
1951 Willys CJ3A/MB/M38 - Little Willy
1995 Cherokee 4.0 - CHEROKEE
1980 Land Rover Series III 109" troop carrier - ROVER
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