Fusible Link size?

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Red Truck
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Fusible Link size?

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I'd like to get verification that I'm doing the right thing: Years ago, I replaced my fusible link because it looked sketchy, and likely prone to failure. After much research, I settled on NAPA p/n 784694 16 gauge replacement. So far, it's been working fine. My question is, is this the correct gauge for the amperage? The truck is stock, with a 50amp alternator, no a/c, no fancy lights or other frills. I'm told the 16 gauge is good for 22 amps, and that the Isuzu color code of red (my old one) for these links is 21 amps. I believe the NAPA 16 gauge link I'm now using is sufficient. Am I wrong? /R
'87 Isuzu p'up 4ZD1/2.3 gas, carb'd, 5spd, 4WD, base model, Fed spec
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Paul
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Re: Fusible Link size?

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I don't think that the ratings for fusible links are as precise as are fuse ratings. That said, the rule of thumb for fusible link wire is that it should be 4 sizes (AWG) smaller than the wire in the circuit it is protecting.

So, it depends on which link you are replacing. There is a blue one (14 ga) that protects a 10 ga glow circuit. Then there is a black one (16ga) that protects a 12 ga circuit. If there is a red link in the truck, I cannot remember where it is or see it on my wiring diagram.

Replacing fusible links with fuses is not recommended. The links generally have a bigger short term overload capability than a fuse. Here is a link to a run down by a company that sells this stuff.

https://www.whiteproducts.com/fusible-faqs.shtml

Paul
'84 P'UP 2 wd diesel, 5 spd with 0.78 fifth gear and differential back to 3.73.
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Red Truck
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Re: Fusible Link size?

Post by Red Truck »

Thanks for the response. As noted, this is for a gas application, and as far as I know, with the single red f-link off the battery. I've seen that Whiteproducts ad before, and lots of other similar info, and I concur with not using anything other than a fusible link. The Isuzu p/n is 894498610 BA, nobody has one, and I've never found what the values are for that link so I can get a matching replacement. A 14 gauge f-link is way larger in physical size than the original, so I settled on a 16 gauge. I still can't verify if this is a proper replacement, and so far I guess I've just been lucky!
Thanx again, and I'll keep looking. /R
'87 Isuzu p'up 4ZD1/2.3 gas, carb'd, 5spd, 4WD, base model, Fed spec
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Paul
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Re: Fusible Link size?

Post by Paul »

Red Truck wrote:
Fri Dec 09, 2022 11:09 am
Thanks for the response. As noted, this is for a gas application, and as far as I know, with the single red f-link off the battery. I've seen that Whiteproducts ad before, and lots of other similar info, and I concur with not using anything other than a fusible link. The Isuzu p/n is 894498610 BA, nobody has one, and I've never found what the values are for that link so I can get a matching replacement. A 14 gauge f-link is way larger in physical size than the original, so I settled on a 16 gauge. I still can't verify if this is a proper replacement, and so far I guess I've just been lucky!
Thanx again, and I'll keep looking. /R
Sorry, didn't notice that you were on gas.

If you still have the original fusible link, you can count the number of wires in the link and measure the individual wire diameter. Then by consulting wire tables you can figure what the resulting wire size is.

Or, you can do it the easy way and look at the wiring diagram for the gas engine in the factory service manual. I just did this and it shows an 0.7mm wire for the red fusible link. This converts to about a # 19 AWG wire. Seems quite small for this application. Especially, since the diesel link for this same alternator 'B' lead wire is shown as a 1.0mm. This is equivalent to about a 17 AWG wire.

The odd number wires are not normally available, especially in stranded sizes and probably not for fusible links either.

The gas alternator 'B' lead wire is 3.0mm as is the diesel alternator 'B' lead wire. So, why the difference in fusible links? Can't say except probably a different engineer. Personally, I would go with the diesel fusible link which is 1.0mm and the closest equivalent AWG size is 16 ga.

Which is what you have, so guess you are good to go.

Paul
'84 P'UP 2 wd diesel, 5 spd with 0.78 fifth gear and differential back to 3.73.
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Red Truck
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Re: Fusible Link size?

Post by Red Truck »

Thanx again for the response. When I replaced the old suspect f-link, it ended up on the road somewhere between here and the post office. I recall placing it on the fenderwell after removing it, took a test drive with the new one, and......yeah, I wish I could've measured the gauge of it. In your first reply, you mentioned your wiring diagram showing wire gauges, and considered asking if it had a 'gas' application section showing same. I have exerpts from the FSM, but not that part. My observation was that an 18 gauge f-link allows about 14 +/- amps, therefore too small, and a 14 gauge link just looked too big. I also could've shaved the insulation off the wire that the f-link taps into (opposite the battery post) to measure it and go 4 sizes smaller, but common sense told me to just go ask somebody. Thanks again for your advice, and I'm a lot more reassured about my f-link choice. /R
'87 Isuzu p'up 4ZD1/2.3 gas, carb'd, 5spd, 4WD, base model, Fed spec
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Paul
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Re: Fusible Link size?

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Red Truck wrote:
Sat Dec 10, 2022 12:16 pm
Thanx again for the response. When I replaced the old suspect f-link, it ended up on the road somewhere between here and the post office. I recall placing it on the fenderwell after removing it, took a test drive with the new one, and......yeah, I wish I could've measured the gauge of it. In your first reply, you mentioned your wiring diagram showing wire gauges, and considered asking if it had a 'gas' application section showing same. I have exerpts from the FSM, but not that part. My observation was that an 18 gauge f-link allows about 14 +/- amps, therefore too small, and a 14 gauge link just looked too big. I also could've shaved the insulation off the wire that the f-link taps into (opposite the battery post) to measure it and go 4 sizes smaller, but common sense told me to just go ask somebody. Thanks again for your advice, and I'm a lot more reassured about my f-link choice. /R
You're welcome.

FYI, ebay does have some factory service manuals and they are very good, covering just about everything.

Paul
'84 P'UP 2 wd diesel, 5 spd with 0.78 fifth gear and differential back to 3.73.
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