fusible links

S

skip hartline

Member
Sep 9, 2011
518
5
18
Evening All,
Just checking over wiring on the right side and noticed the fusible link was showing its telltale age by the insulation backing away from the ring
terminals. I know the fusible link has been a standard for years to protect the main power feed to the ignition switch and other power users. It has
always seemed like it would be a choke on current flow when your feeding a 12 ga load with 16 ga wire. The old saying I learned years ago is "that
it's easier to pour water in a bucket than a coke bottle". So my question is has anyone replaced the fusible link with a circuit breaker or some other
type of load protection? I'm going to be replacing the link one way or the other, just wonder if a better ideal has been tried and proven. Thanks in
advance.
Skip Hartline
 
I would say that if a device has protected your wire harness from failure,
and not burned your coach to the lug nuts in so doing, that it must be
sized appropriately for the task at hand. However, if the ampere flow has
been increased by added loads, it might be time to up grade to the next
size. Stuff that just sits there and has no moving parts usually are the
most reliable.
Jim Hupy

> Evening All,
> Just checking over wiring on the right side and noticed the fusible link
> was showing its telltale age by the insulation backing away from the ring
> terminals. I know the fusible link has been a standard for years to
> protect the main power feed to the ignition switch and other power users.
> It has
> always seemed like it would be a choke on current flow when your feeding a
> 12 ga load with 16 ga wire. The old saying I learned years ago is "that
> it's easier to pour water in a bucket than a coke bottle". So my question
> is has anyone replaced the fusible link with a circuit breaker or some other
> type of load protection? I'm going to be replacing the link one way or the
> other, just wonder if a better ideal has been tried and proven. Thanks in
> advance.
> Skip Hartline
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Find the amperage rating of the fusible link in the manual or wiring diagram, or perhaps one of the GMCers on the net knows what the rating is.
Probably 40 or more amps. Then go to your favorite car stereo shop and get a modern fuse holder capable of handling 150% of that current, but only get
a fuse for the same current rating as the fusible length rating or just a few amps more (maybe 10 more amps). Replace the aged fusible link with that
and that will protect your existing wiring. If you need to add more loads to the system in the future, the best way will be to add another fuse setup
to power those loads separately from the fusible link circuit you are repairing now.
--
Terry Kelpien

ASE Master Technician

73 Glacier 260

Smithfield, Va.
 
A fusible link was never designed to be a fuse and easily replacable. It was designed as a safety device that will burn in two in case of an short in
an area not protected by a fuse. This is primarily the inputs to all fuses meaning the wiring harnesses. You should not be replacing this until you
find what caused hte extreme current overload.

Real fusible link wire is suppose to contain the flame or spark generated inside the isulation when the link burns in two.

There is no amp rating for fusible links, or at least I have never seen one. In general they say to use a fusible link wire 4 gauge sizes below the
size of the wire that would normally be sued for that load. So if a 10 gauge wire is what you would require to support that load, then a 14 ga.
fusible link would be used to protect that harness or load.

In our case the largest wire fed by the fusible link is 12 ga. so a 16 ga. is appropriate and what GM used.

This is probably more than you really wanted to know.

I suggest that you replace a bad fusible link with one of the same gauge and length. Ours is 16 gauge.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
YES

> A fusible link was never designed to be a fuse and easily replacable. It
> was designed as a safety device that will burn in two in case of an short in
> an area not protected by a fuse. This is primarily the inputs to all
> fuses meaning the wiring harnesses. You should not be replacing this until
> you
> find what caused hte extreme current overload.
>
> Real fusible link wire is suppose to contain the flame or spark generated
> inside the isulation when the link burns in two.
>
> There is no amp rating for fusible links, or at least I have never seen
> one. In general they say to use a fusible link wire 4 gauge sizes below the
> size of the wire that would normally be sued for that load. So if a 10
> gauge wire is what you would require to support that load, then a 14 ga.
> fusible link would be used to protect that harness or load.
>
> In our case the largest wire fed by the fusible link is 12 ga. so a 16 ga.
> is appropriate and what GM used.
>
> This is probably more than you really wanted to know.
>
> I suggest that you replace a bad fusible link with one of the same gauge
> and length. Ours is 16 gauge.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://bdub.net/gmcmotorhome.info/
Alternator Protection Cable
http://bdub.net/gmcmotorhome.info/APC.html
 
Here is an article on fusible links from a site for Amateur Airplane
Builders:
http://www.aeroelectric.com/articles/fuselink/fuselink.html

> Find the amperage rating of the fusible link in the manual or wiring diagram, or perhaps one of the GMCers on the net knows what the rating is.
> Probably 40 or more amps. Then go to your favorite car stereo shop and get a modern fuse holder capable of handling 150% of that current, but only get
> a fuse for the same current rating as the fusible length rating or just a few amps more (maybe 10 more amps). Replace the aged fusible link with that
> and that will protect your existing wiring. If you need to add more loads to the system in the future, the best way will be to add another fuse setup
> to power those loads separately from the fusible link circuit you are repairing now.
 
10-4, I just was interested if something was found to be better, not trying to reinvent the wheel, like most everything, simple is usually better. The
old KISS saying "Keep It Simple Stupid" works. Thanks for the answers and insight.
Skip Hartline
 
The problem with using a fuse holder is that the engine compartment
gets hot and a plastic fuse holder will melt and the fuse will fall out.
Ask me how I know.

I would stay with the factory designed 16ga fusible link wire.
--
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
 
Any fuse holder that holds a 40-60-100 amp fuse is not going to melt unless you mount it right on the engine or over the exhaust system. The fuse
holder should not be near that much engine heat, and if you mount it where there is that much heat then you should not be working on this stuff at
all. Don't use the little plastic inline fuse holders for anything except the CB radio that it came on. Those things are only good for 10 amps MAX and
I have seen several melt with a 2 amp load due to the spring load on the fuse and the slightest oxidation of the contacts or the fuse ends.

The fusible links are the worst electrical protection device ever installed on any vehicle by any manufacturer, being nearly impossible to find most
of the time and unrepairable to proper safety and conductivity standards. They melt adjacent wiring in harnesses and cause more damage than they
prevent. Their only saving grace is that end users of the vehicles have no idea they are there and consequently don't get the chance to mess with them
and substitute pennies and gum wrappers for them when they overload like they do for fuses. Idiots WILL substitute regular wire for them if they find
them blown and then burn the car on the side of the interstate.

Professional technicians have to tear apart the wiring harness in inaccessible locations just to get to them, frequently next to the bulkhead
connector. BTDT, and spent the 4 hours repairing the damage done to the rest of the wiring next to the link. Horrible, horrible things that should not
be on any vehicle unless they are out in the open, isolated from other wiring, readily accessible, testable, and repairable. Smart manufacturers now
put the large fuses in a proper enclosure near the battery, not in a wiring harness buried somewhere else in the vehicle. And they have designed the
fuses now so improper substitutes do not fit in the fuse box. Many of the larger current fuses are now fastened in with screws and the boxes are
weather-sealed.

The large fuse holders with gold contacts from the car stereo shop will handle much more heat than is present near the batteries or under the front
hoods of the GMC. The best ones will have screws to fasten the fuse, and those fuses will cost more, but if you are running high current (like the
charge wire from the alternator), that's what you want.

--
Terry Kelpien

ASE Master Technician

73 Glacier 260

Smithfield, Va.
 
Any NAPA auto supply sells fuse wire. It's cheap. A spool is less than $10.
Fuse wires are used extensively throughout the auto industry for a reason.
They protect the wiring harness from burning up. I can't understand
why some people think fusible links are poor design. These
people don't know much about electrical circuitry.

The plastic fuse holders from O'Reilly Auto are weak and do not work.

--
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
 
I once replaced the fusible link with an O'reilly Auto fuse holder and a 30 amp fuse.
The fuse holder was mounted in the same location where the fusible link goes.

I went dry camping on a 100+ degree day, arriving late at the campground. When
I stopped and hit the brakes, everything went dark, no headlights, no ignition.
The fuse holder was hot and fell apart.

I went back to the 16ga fusible link and haven't had a problem since.
--
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
 
> ...Fuse wires are used extensively throughout the auto industry for a reason.
> They protect the wiring harness from burning up. ...
Hmmm. Does anybody else see conflicting information between this post and the info at the following URL?

http://www.gmcmotorhome.info/engine.html
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Highest price does not guarantee highest quality."
 
We are talking about two different things. The 10 ohm nichrome wire is in the alternator control circuit and burns due to an alternator over voltage
failure. It has nothing to do with an unfused short to ground that the fusible link is protecting from.

The nice thing about the fusible link in a GMC is it is NOT buried in a wiring harness somewhere. It is easily to see, access, and change if
necessary. You can get another one at Autozone that is pre-cut and ready to go for $3.00 or $4.00 I forget if it already has the end lugs on it or
not. It can be changed in minutes.

I have only changed 3 or 4 of them in my life and all of them were were easy to change on GM vehicles. I have no idea how other brands implement
fusible links.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
> The problem with using a fuse holder is that the engine compartment gets hot and a plastic fuse holder will melt and the fuse will fall out.
> Ask me how I know.
>
> I would stay with the factory designed 16ga fusible link wire.

Bill,

Good fuse holders are Bakelite. They will burn before they melt.
But, a properly done fusible link is a known issue.

Matt

--
Matt & Mary Colie - Members GMCMI, GMCGL, GMCES
'73 Glacier 23 - Still Loving OE Rear Drum Brake with Applied Control Arms
Now with both true Keyless and remote entry
SE Michigan - Twixt A2 and Detroit
 
"Probably 40 or more amps. Then go to your favorite car stereo shop and get a modern fuse holder capable..."

If open a book and read the current capacity of 12 gauge stranded copper wire you will find that it's 16-20 amps.
--
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
 
That is the capacity before the wire starts generating heat.
--
Terry Kelpien

ASE Master Technician

73 Glacier 260

Smithfield, Va.
 
I have not had any problems using that type of fuse holder as long as it is good quality construction, connected with a good quality crimp connector
(or soldered to the connector), and kept out of the weather. Do not use them for more than 30 amps, and a continuous load of 30 amps is actually about
5 over the limit that will start to generate heat in the wire and the female spade connectors that the fuse plugs into. Always engineer your systems
for 150% of normal load and they will serve you well, no matter what type of system it is. If you are working on airplanes or submarines, engineer for
200% of normal load because failure may cancel your return trip or accelerate it beyond your control!
--
Terry Kelpien

ASE Master Technician

73 Glacier 260

Smithfield, Va.
 
The ones that I use have a heavier gauge wire on them, maybe it's 10 instead of 12. As you said before, 20 amps should be the greatest CONSTANT load
passed through that holder and the 12 gauge wire. The 30 amp fuse will handle a short pulse or startup current, but if you need 30 CONTINUOUS amps
flowing, step up to a higher grade of fuse holder.
--
Terry Kelpien

ASE Master Technician

73 Glacier 260

Smithfield, Va.
 
My understanding is that a fuse has a small thermal mass designed to blow quickly once the rating (current and time) has been exceeded. A fusible
link has a large thermal mass designed to take large over-currents for short periods of time but will finally give out and protect the wiring harness
in the case of catastrophic failure (ie accident). Its insulation is designed not to melt through or burn.

The fusible link feeds the electrical system through individual fuses which protect their circuit and equipment. The fusible link is the final point
of protection. Replacing it with a large fuse may cause that fuse to fail due to repeated short period over-currents, but not enough to blow the
fuse.

If a fuse holder melts, it was likely caused by a poor electrical connection to the fuse.

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
Hubler 1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
 
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