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Old 12-18-2020, 07:24 PM   #1
crossy
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wiring harness specifics, what AMP fuse? 1987 K5

As the title says, fixing this harness from an 87 K5. See the area circled in blue coming off the 12V junction, looks to be orange 14 gauge to a fuse then 12 gauge red. (my guess) i want to know what amp that fuse is or is the whole orange wire the link. Wanting to fix the varmit chews, but would rather replace that fuse with something more common. My local autoparts carries fusible links, but prefer to make it a replaceable.
All the harness diagrams I found on line just state that it is a fusible link.
thanx, Crossy
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Old 12-18-2020, 07:55 PM   #2
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Re: wiring harness specifics, what AMP fuse? 1987 K5

Where does that particular wire go? Guessing anywhere from 20-30a at least, given the size of the wires.
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Old 12-18-2020, 08:58 PM   #3
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Re: wiring harness specifics, what AMP fuse? 1987 K5

This is all I could find on the orange wire. I’m thinking the whole orange wire is a fusible link.
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Old 12-18-2020, 09:04 PM   #4
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Re: wiring harness specifics, what AMP fuse? 1987 K5

The small wire is the fusible link, it's smaller than the wire it protects so it melts before the main wire does. The black part is just the connector.
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Old 12-19-2020, 03:39 PM   #5
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Re: wiring harness specifics, what AMP fuse? 1987 K5

so what would be the melting amperage of the orange wire? lol
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Old 12-19-2020, 06:24 PM   #6
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Re: wiring harness specifics, what AMP fuse? 1987 K5

Quote:
Originally Posted by 44th Miss Inf View Post
This is all I could find on the orange wire. I’m thinking the whole orange wire is a fusible link.
That's a 1mm fusible link. The plastic is molded over the splice between the fusible link and the actual wire by whomever GM had building these harnesses... Precision, Blaylock, ....
That looks just fine.

That could be one of the main cab power connections, your AC blower HI power wire or one of your alternator connections.
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Old 12-21-2020, 09:18 AM   #7
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Re: wiring harness specifics, what AMP fuse? 1987 K5

There's a reason they use fusible links and not a fuse.
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Old 12-21-2020, 10:38 AM   #8
hatzie
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Re: wiring harness specifics, what AMP fuse? 1987 K5

Fusible links are ultra slow blow fuses that are more difficult to replace than fuses by design... for lack of a better description.
They have a specific design purpose that they are uniquely suited for.

What Am I saying?
They are time consuming to install on purpose. This forces the owner to discover what's causing the large current draw instead of slapping a larger fuse in place and eventually setting fire to the vehicle. This is not the main purpose of using them just a happy side effect...
These circuits also usually contain "high inrush current" devices like tungsten filament lamps and electric motors that draw significantly more power on startup than they do while running. Alternators fall into that category as well since a fairly depleted battery sucks up a big slug of current when charging starts before nearly instantly settling at a lower charge current. Look at your battery charger analog Ammeter needle. It swings high and settles down lower almost instantly when you switch on the charger.
Those large inrush currents will burn out regular fuses after several (10-30) cycles and circuit breakers don't like it either if they aren't rated for electric motor duty. Fusible links can be rated a lot closer to the running current of the attached devices without being overly stressed by a second or less of high inrush. This way when the circuit starts to draw more current continually than it should it will burn up the link rather than the attached wiring harness or device.
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1959 M35A2 LDT465-1D SOLD
1967 Dodge W200 B383, NP420/NP201 SOLD
1969 Dodge Polara 500 B383, A833 SOLD
1972 Ford F250 FE390, NP435/NP205 SOLD
1976 Chevy K20, 6.5L, NV4500/NP208 SOLD
1986 M1008 CUCV SOLD
2000 GMC C2500, TD6.5L, NV4500
2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263
2009 Impala SS LS4 V8


RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...Please include at least the year and model in your threads. It'll be easier to answer your questions.
And please let us know if and how your repairs were successful.

Last edited by hatzie; 12-21-2020 at 10:52 AM.
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