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Fuseable Link on 1994 Chevy 3500

W

Walter Buller

Member
On my 3500 diesel dually, there are 5 bolts on the upper left side of the firewall. They each have a fairly heavy wire attached to them. Each wire has
a white, round fuseable link in line before joining the wiring harness. One of those fuseable links finally failed. I can't find them, but I did find
a kit at O'Reilly's that contains about an 8 gauge copper wire with an inline 30 amp round fuse inside of a white plastic housing. But as soon as I
installed it and cranked the Cummins motor, the fuse burned. The truck runs just fine with no inline fuse on that line. The alternator gauge shows 14-
15 volts. Do any of you know what amperage this in-line fuse should be? Thanks for your comments.
 
The fusible link is there to protect the wire it is connected to. Check the diameter/gauge of the wire for an idea of the maximum current the wire can handle.

If the wire has been re-purposed in the Cummins conversion, look at the current needs of the new application. The wire may need to be upsized for the new application.
 
Dig up a wiring diagram and see what that line is feeding so you can track down and repair the problem otherwise all you are going to do is spend a bunch of money on fuses.

The fuseable link portion of the wire is basically just a piece of wire 4 gauges smaller than the wire it is protecting covered with a piece of non burnable insulation.

They are supposed to be able to handle momentary spikes better than a fuse will but given the description of what yours is doing, a wire is probably pinched, burnt or missing insulation which is causing a direct short to ground.

The link burns up so your truck doesn't and installing a fuse with a higher rating than what the wire is rated for potentially can lead to a fire.
 
When that wire is disconnected from the firewall, EVERYTHING on and in the truck works perfectly, except the alternator, so let's assume that this
wire is dedicated to the alternator and only the alternator, because that is apparent. The in-line fuse kit I bought at O'Reilly's and installed in
place of that wire did no good at all. The first 30 amp fuse in it burned as soon as I cranked the motor. The second 32 amp fuse caused the alternator
to burn up. This was confusing to me until I called my son. He has been supervising the maintenance on heavy equipment for about 15 years. He said
older model Chevy's like mine used "Slo-Blo" fuses in that application. I had never heard of such a thing. He said they are designed to regulate
spikes in alternator current while maintaining the flow of the current so nothing shuts off. He said that by installing a typical round, glass 30-32
amp fuse I had subjected the alternator to fluctuations in current that it was not designed for, hence ruining it. Well, now I know.
 

When a fusible link blew on my 92 Dodge I decided to replace them all with fuses. I used a marine grade fuse box.

mvphoto43551.jpg


mvphoto43552.jpg
 
Great idea. Do you know the amperage rating on those fuses? I finally installed a 50 amp circuit breaker on that wire. Works just fine.
 
There is a color code with the amp rating for the fusible links, I just replaced each fusible link with a fuse of the same amperage.
I will see if I can find a link to the color code and post it later today.
BTW - The fuse panel I used did not include any fuses.
 
It looks like your best bet would be to determine the gauge of the fusible links you want to replace and then determine the amperage of the link based on the gauge of the wire. I wish there was an easy answer, but it looks like different auto manufactures may have used different colors for their fusible links.
 
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