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Bionicdodge.Com  |  Bionic Tech  |  Stereo & Electronics (Moderator: magnumman)  |  Topic: fusible link alternative? 0 Members and 1 Guest are viewing this topic. « previous next »
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donram360
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« on: May 05, 2020, 01:27:00 PM »

ok here goes again... I swore I posted a topic about this a couple days ago here but cant find it?   Casualty of being a computer idiot....  and partly why I am posting about work I am doing to a truck made in 1985 haha... 

I'm working on an old 85 Dodge D150.  The wiring harness on it is a horror story, lots of previous owner interference and butchery.... I have never seen such a butchered harness on 1 vehicle, at least a couple old vehicles' worth of butchered hacks....that I am working on undoing.

This is an old inline 6 (225 cu in "slant" 6) "old man's truck" 6 cyl, carbureted, AT, crank windows, no AC, etc...but the body id decent so I'm gonna try to make something of it

Part of the problem, [and many old vehicles had these, not just Dodges] pertains to "fusible links". This truck has 4-5, and a couple of those are blown. If this was the "only" harness damage I'd fix this harness and run it. But I'd still incorporate my idea that I am doing, with the replacement harness I got from the junkyard, even so.
The best harness available of ~4-5 to pick from locally, is off of a 1984 truck.  and it has its share of age related deterioration, (cracked insulation, bare spots, etc) but nowhere near as bad as the original.
I have fixed almost all of the deterioration (not as bad as fixing butchery like the original)  except it, too, has a couple of bad fusible links. Yes/ I know Napa has "fusible link wire" available. but 4 of them on this truck, branch into 1 main splice,  that goes  straight to the battery. I'd still have to add a bus bar of some type to tie them into that main "hot".

I went back to the junkyard, looking for an idea. Newer cars and trucks have several fuse boxes, including one under the hood where the main heavy loads are branched from. I wound up with one from a 90-92 Ranger, I didn't want anything big and unwieldy like many of these fuse boxes are. The one I have, has all "maxi" style fuses in it, 10 or 12 spots and 2 regular blade style "ATO" fuse slots.  Enough for a few "spares" for possible future add ons.
My problem, is that fusible links do not have an "amp rating" but they are 4 gauge sizes smaller than the "parent" circuit wiring. All I can find is a color chart that tells what the standard colors are for a given gauge size of fusible link. Nothing at all about an "amp" rating. I have wasted lots of Google time going in circles looking for this.
I did find this, from Littelfuse, (Ok, computer idiot trying to post a link, wish me luck.... ) https://www.littelfuse.com/data/en/technical_articles/tb98-001.pdf#page=1
that says that these maxi fuses were designed just for this reason/purpose.... rated in AMPS... not some other scale.  so how do I translate a fusible link to amp capacity?
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magnumman
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« Reply #1 on: May 05, 2020, 04:05:12 PM »

Hopefully this helps you.

18 gauge fusible links are rated at 14 gauge wire or 15 amps , 16 gauge are rated at 12 gauge wire or 20 amps. The fusible link that protects the wire should then be two gauge sizes (or four numbers larger).

(4 numbers larger) actually means lower by counting.  Gauge size goes lower as wire gets larger.

So 20 gauge fusible link would be rated at 16 gauge wire or 10 amps.

« Last Edit: May 05, 2020, 04:12:55 PM by magnumman » Logged

2001 Ram QC 1500: 360cid, 2wd, K+N CAI, SCT tune, Autolite AP3923\'s, MP 1.7 rollers, MP pushrods, SST rims, Hypertech coil, 10.2mm wires, Gibson super truck exhaust, 3\" magnaflow cat, modified Y pipe, modified kegger, 3.92 LSD, MSD-6, Transgo shift kit, 4.7L Injectors, Hipotek 52mm TB, (Currently under construction for a 408 build)

POS Chevy Trailblazer 4x4, the 4x4 is the only good part. This is my Son's truck now.

2007 Chrysler 300 2.7L "Wifes car" No complaints other than it slow.

2012 Ram 5.7 Hemi Outdoorsman, 4x4, LSD, Air Bag Suspension.
magnumman
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« Reply #2 on: May 05, 2020, 04:24:41 PM »

For odd gauge numbers its the same principal.

21 gauge fusible link would be rated at 17 gauge wire or 7.5 amps.

22 gauge fusible link would be rated at 18 gauge wire or 5 amps
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2001 Ram QC 1500: 360cid, 2wd, K+N CAI, SCT tune, Autolite AP3923\'s, MP 1.7 rollers, MP pushrods, SST rims, Hypertech coil, 10.2mm wires, Gibson super truck exhaust, 3\" magnaflow cat, modified Y pipe, modified kegger, 3.92 LSD, MSD-6, Transgo shift kit, 4.7L Injectors, Hipotek 52mm TB, (Currently under construction for a 408 build)

POS Chevy Trailblazer 4x4, the 4x4 is the only good part. This is my Son's truck now.

2007 Chrysler 300 2.7L "Wifes car" No complaints other than it slow.

2012 Ram 5.7 Hemi Outdoorsman, 4x4, LSD, Air Bag Suspension.
donram360
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« Reply #3 on: May 06, 2020, 07:28:52 AM »

Sorry not really. The hot off of the alternator is a 10 ga for either (not sure which) either a 60 or a 78 amp alternator, has a 14 ga fusible link closer to the battery,
The fuse box I have to go in there has a 60a as its biggest fuse and 10 ga wire coming from it.
I don't have a factory service manual for that year but the ones that I have are 2 years either way from 85. And the (gulp) Haynes that I have showed 81-84 being the same as each other, (doesn't extend to 85) and it has 10 ga as being the main hot off of the alternator except for the 100a option which goes to 6ga.
As it is from the factory, there is a short 6 ga coming off the battery which splits to 4 fusible links the heaviest on the other side of the links are 2 10 gauge. The other ones are like a 14 and a 18 (not counting the links)
I too have seen several charts that tell how many amps each wire gauge is good for and I tell you what, according to those about half of a cars wiring harness should be 6 ga or heavier, and many battery cables I see on vehicles at work might have 3 or 4 on the whole vehicle that heavy.  Is it because at lower voltage the amps can be more? Going by those charts  surprised that there aren't a whole lot more car wire fires especially as more and more crap (much of which is unneeded BS)  is added to them, the newer they get.
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donram360
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« Reply #4 on: May 06, 2020, 04:42:45 PM »

For years the main hot starter cable on older Dodge's was only 6 ga, and the starters draw 150 amps on a good day, not counting initial surge.
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magnumman
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« Reply #5 on: May 07, 2020, 04:28:59 PM »

This is just my opinion since I do DC electrical work for a living.  Just because I posted the link size vs wire size doesnt mean thats the size of wire you have on the truck.

Do you know the gauge of the Fusible Links?  If so, what I posted above will be the AMP of the fuse you want to put in based on the gauge size of the Link.  Or if you know the size of the wire
 the fuse size to replace the Fusible Link would be opposite of what I posted above. Just subtract 5 amps (or 2.5 amps for odd numbers) from what the wire gauge on the truck is rated for and thats your fuse size. 

For example:

14 gauge wire=10 amp fuse
12 gauge wire= 15 amp fuse
17 gauge wire= 5 amp fuse
Usually 5 amps is the lowest no matter gauge, I think Ive seen a couple 2.5 amp fuses but I dont remember the wire size.

The goal is to have the fuse lower than what wire can handle.
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2001 Ram QC 1500: 360cid, 2wd, K+N CAI, SCT tune, Autolite AP3923\'s, MP 1.7 rollers, MP pushrods, SST rims, Hypertech coil, 10.2mm wires, Gibson super truck exhaust, 3\" magnaflow cat, modified Y pipe, modified kegger, 3.92 LSD, MSD-6, Transgo shift kit, 4.7L Injectors, Hipotek 52mm TB, (Currently under construction for a 408 build)

POS Chevy Trailblazer 4x4, the 4x4 is the only good part. This is my Son's truck now.

2007 Chrysler 300 2.7L "Wifes car" No complaints other than it slow.

2012 Ram 5.7 Hemi Outdoorsman, 4x4, LSD, Air Bag Suspension.
donram360
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« Reply #6 on: May 08, 2020, 02:55:26 AM »

I don't see how 60 a from the alternator thru a 10 ga wire will let a 20a fuse survive. But that's why I am not an electrician
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magnumman
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« Reply #7 on: May 08, 2020, 06:45:42 PM »

I don't see how 60 a from the alternator thru a 10 ga wire will let a 20a fuse survive. But that's why I am not an electrician

Ten gauge wire is 30 amp rated capable so it would require a fuse less than that, so 25 amp fuse based on a general rule. But not in your case because your footage is much smaller than general rule.

 On an estimation I'm gonna say your alternator wire is 4ft long "the math comes out perfect with 4ft vs 60amps at 12volts = 10 gauge wire".  So a 50-55amp fuse would work for your alternator fuse to protect the 60 amp wire.

Everything I posted above will work for everything leaving the fuse box.

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2001 Ram QC 1500: 360cid, 2wd, K+N CAI, SCT tune, Autolite AP3923\'s, MP 1.7 rollers, MP pushrods, SST rims, Hypertech coil, 10.2mm wires, Gibson super truck exhaust, 3\" magnaflow cat, modified Y pipe, modified kegger, 3.92 LSD, MSD-6, Transgo shift kit, 4.7L Injectors, Hipotek 52mm TB, (Currently under construction for a 408 build)

POS Chevy Trailblazer 4x4, the 4x4 is the only good part. This is my Son's truck now.

2007 Chrysler 300 2.7L "Wifes car" No complaints other than it slow.

2012 Ram 5.7 Hemi Outdoorsman, 4x4, LSD, Air Bag Suspension.
donram360
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« Reply #8 on: May 18, 2020, 10:08:51 AM »

Well it's back up and running again, starts easy, everything works, no magic smoke and no more fusible links.
I'd do it again if I had to
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magnumman
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« Reply #9 on: May 18, 2020, 04:14:07 PM »

Glad you got it going!
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2001 Ram QC 1500: 360cid, 2wd, K+N CAI, SCT tune, Autolite AP3923\'s, MP 1.7 rollers, MP pushrods, SST rims, Hypertech coil, 10.2mm wires, Gibson super truck exhaust, 3\" magnaflow cat, modified Y pipe, modified kegger, 3.92 LSD, MSD-6, Transgo shift kit, 4.7L Injectors, Hipotek 52mm TB, (Currently under construction for a 408 build)

POS Chevy Trailblazer 4x4, the 4x4 is the only good part. This is my Son's truck now.

2007 Chrysler 300 2.7L "Wifes car" No complaints other than it slow.

2012 Ram 5.7 Hemi Outdoorsman, 4x4, LSD, Air Bag Suspension.
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