Is this a fusible link and what connector is this?

[AllGoNoShow]

I am redoing all the battery cables in my 68 C10 and came across this red wire that previous owner had connected to the battery-it looks like it’s 16g but the insulation isn’t thick like a typical fusible link I’ve seen. It also appears to be about 18 + inches long until it jumps up in size to the 12g wire that goes across the radiator shroud. In about the same area there is the below, unused connector that comes out of the wiring harness…anyone know what this is?

It is my understanding that stock these trucks had a junction block which the fusible link attaches to but I don’t necessarily need/want to recreate that. If someone just added an 18 inch section of 16g wire will that function as a fusible link or is that too long and should I just replace with an actual labeled fusible link?
Posted via Mobile Device

[HotWheelsFan]

Two things about fusible link wiring, the wire is a special type along with the insulation. Fusible link wire should have specs printed on the insulation.

So, in your case it appears the red wire is copper with thin plastic insulation. Doubtful it being a fuse link.

White connector does not look familiar. Look to see if it is for the front turn or side marker light connector maybe?

[AllGoNoShow]

Dug a little deeper and removed a bunch of electrical tape and that wire is like more than 2 feet long before it jumps up to the 12g wire that goes to the fuse panel for power. It is going to get torn out and a proper fusible link it it’s place.
Posted via Mobile Device

[MikeB]

Originally Posted by AllGoNoShow

Dug a little deeper and removed a bunch of electrical tape and that wire is like more than 2 feet long before it jumps up to the 12g wire that goes to the fuse panel for power. It is going to get torn out and a proper fusible link it it’s place.

Crazy. Some previous owner must have thought he was replacing a standard wire!

Some good info here: https://www.whiteproducts.com/fusible-faqs.shtml

Also, wherever you can replace a length of 12 gauge wire with 8 gauge or even 10 gauge, you will have less resistance along that wire so you'll see higher voltage at the battery when it's charging. You'll also see higher voltage at the headlights and other lamps.

I'll be installing an AAW wiring harness in my 69 very soon, and it uses 6 gauge wire and a fuse for the charging circuit, and 10 gauge to feed the fuse panel. https://www.americanautowire.com/med...20IN%200.0.pdf It's overkill for most of us, but voltage drop along those wires is essentially nil.

[AllGoNoShow]

Originally Posted by MikeB

Crazy. Some previous owner must have thought he was replacing a standard wire!

Some good info here: https://www.whiteproducts.com/fusible-faqs.shtml

Also, wherever you can replace a length of 12 gauge wire with 8 gauge or even 10 gauge, you will have less resistance along that wire so you'll see higher voltage at the battery when it's charging. You'll also see higher voltage at the headlights and other lamps.

I'll be installing an AAW wiring harness in my 69 very soon, and it uses 6 gauge wire and a fuse for the charging circuit, and 10 gauge to feed the fuse panel. https://www.americanautowire.com/med...20IN%200.0.pdf It's overkill for most of us, but voltage drop along those wires is essentially nil.

Hmmm, good to know. Does that wiring harness even use a fusible link or like a maxi fuse? Thinking about just using a maxi fuse instead of fusible link now, but don’t know what amperage I would need to protect the stock 12g wire? 25-30amps maybe?
Posted via Mobile Device

[dmjlambert]

I understand the point of the fusible link is to burn up first instead of burning up your main truck wiring, and when it does burn the insulation on it melts and smokes but doesn't burst into flames.

If you go changing the wire sizes, you may need to be aware the stock battery gauge is an ammeter and it depends on the battery to alternator junction wire being 12 gauge. That length of wire across top of the radiator support serves as a shunt. Some people don't mind that because they don't have a working ammeter or they have replaced it with a volt meter. Or may not have a gauge type instrument cluster.

Probably the safest and easiest way is to use fusible link wire. It should be 2 wire sizes smaller than the smallest non-fuse-protected wire, which is 4 wire numbers higher. On a stock truck the non-fuse-protected wires are all 12 gauge, and are protected by a 16 gauge fusible link wire about 6 to 9 inches long. If parts of your wiring are something bigger, such as 8 gauge, you will still need a 16 gauge fusible link because some of the wiring in the cab that is not fuse-protected is still 12 gauge.

Your truck sounds very much like the way I found my truck when I bought it. I spliced a couple feet of 12 gauge red wire onto the red wire that was coming through the wire holder that goes across the top of the radiator, to make it long enough to reach the junction block by the battery (like it once did when the truck came from the factory). I used a solder connection with heat shrink tubing to splice it.

[MikeB]

Originally Posted by AllGoNoShow

Hmmm, good to know. Does that wiring harness even use a fusible link or like a maxi fuse? Thinking about just using a maxi fuse instead of fusible link now, but don’t know what amperage I would need to protect the stock 12g wire? 25-30amps maybe?
Posted via Mobile Device

I'm not quite sure how to determine a maxi-fuse size, but it should be more than your maximum alternator output. But then again, I've read where a 16 gauge fusible link can handle 22 amps. Seems kind of strange because stock 1968 alternator probably made at least 40 amps.

On the last AAW wiring harness I installed, I decided to use 8 gauge wire instead of the 6 gauge in the kit because I didn't have much current draw from accessories. And the alternator was rated at only 78 amps. Also, the fat 6 gauge wire is a little hard to route! Anyway, the AAW tech guy suggested a 100 amp fuse for that setup.

In the attached photo, the left 8 gauge wire goes to the battery terminal on the starter. The two fused wires on the right go to the alternator output terminal and to the fuse panel "battery" bus.

[MikeB]

Originally Posted by dmjlambert

If you go changing the wire sizes, you may need to be aware the stock battery gauge is an ammeter and it depends on the battery to alternator junction wire being 12 gauge. That length of wire across top of the radiator support serves as a shunt.

Good catch. I'd forgotten about that. Very few folks actually understand how that works, and some think it's a full-current ammeter. My 69 has a voltmeter from an 80-something truck.

[pjmoreland]

That connector looks like it's for the original 10DN externally regulated alternator.

[Accelo]

1972 alternator is 37A
with AIR its 42A
Motor Home was 61A.

Anytime you increase the alternator output, past what the stock wiring capacity will handle, the wiring between the alternator and battery will have to be replaced. Then the stock amp gauge will cease to function. No big deal as most have too much resistance, in the wiring and connections, to work after 50 years anyway. You can test it by turning on the head lights without the motor running. Typically they will jump a little and go back to 0 amps or not move at all. This is one of the many reasons GM went to a volt gauge instead.

[AllGoNoShow]

Well good to know about the ammeter not working. The alternator is an upgrade (I had it laying around on my camaro but its a stock application for an 80s car as I remember and puts out 100+) and I also just upgraded the alternator charging cable to 6 gauge while I was at it.

Did these trucks come with a fusible link at the 12g purple starter wire (my 2nd gen camaros had them here) as well?, or is the fusible link at the battery that feeds the fuse panel essentially cover that wire as well?

[HO455]

On a 37 amp standard alternator there is only the one fuseable link.

Normally fuses are sized 25% over the maximum expected current of the circuit. The problem on changing circuits is that if you have a 50 amp alternator wired with 8 guage wire then the fuse should be 62.5 amps by the math. So you would choose a 60 amp fuse.
The fuse will provide short circuit protection but not over current protection.

If your battery is demanding 54 amps the 8 guage wire from the alternator will be carrying more amperage than it is rated for. (Most alternators will supply more amps than they are rated for.) Eventually if this condition continues the installation on the wire will fail, causing a short circuit. By the time the melted insulation causes the fuse to blow the damage is already is done to the wiring.
If you replace the 60 amp fuse with a 50 amp fuse every time the alternator goes to full charge rate the fuse will blow. An annoying condition at the least.

At this point you have 2 choices replace the 8 guage wires with 6 guage or replace the fuse with a fuseable link.

Up the sized wiring would give you a very robust harness but at a greater cost.

The correctly sized fuseable link will give the circuit the overcurrent protection it needs and give adequate short circuit protection. By adequate I mean if the harness gets shorted to te frame it will take several seconds for the fuseable link to melt cutting off the connection to the battery. There might be additional damage caused by that delay but it should prevent the truck from catching fire.

For some reason on our trucks GM installed an insulated post in the circuit to make replacement of the fuseable link easier. Something they didn't do on cars of the same era. We could speculate for hours on why they made the decision to spend the extra money. If you want to delete the insulated post on your truck there won't be a problem.

I'm just trying to provide some information on things to consider when you make changes to your factory wiring. We've all seen pictures of restored or modified vehicles on fire. You never hear the reasons why but I would bet most start as a result of improper wiring.

Please do not use the example I listed to make choices for your system. It is a simple example to help explain the considerations involved.