Melted Fuse

JMT

JMT

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I’ve got some electrical problems I could use some help on. Instrument cluster back lights don’t work. Fuse #10 (Instrument Cluster) is good and getting current. I pulled the instrument cluster and unplugged both plugs just to make sure they were seated. Plugged back in with no change. Turn signal indicators work, check engine works, et Al, but no backlighting.

Fuse #1 was glowing and I removed the fuse quickly. It was extremely hot and blown. I put another fuse in and the sequence is it gets hot and starts melting the plastic, then blows the fuse, but keeps glowing and melting the plastic. I cleaned the fuse blades and fuse holder as well as I could with no change. When I put a new fuse in I see a spark in the input side and it Immediately gets hot.

Fuse #4 (door defeat) is good, but no current passing through the fuse (is this normal?) When passenger door ajar there are three sets of double beeps and then nothing. When driver door ajar it beeps as normal till the door is shut. Any ideas appreciated.

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I’ve read that:

If the tension in the fuse holder is not good then the connection will not be good, and heat will build which can blow the fuse.

Aluminum oxide can also build up on the fuse blades causing a poor connection with the same result.

Not sure how to fix the tension in the fuse holder. I can get better fuses with a thicker blade for a better connection, but the original fuse was a good fuse. Some of the others I tried were lower quality Amazon bulk.
 
joniki said:
I agree. I have to ask what size fuse is supposed to be in there? The yellow fuse is typically 20 amps.
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How does any of that change the precise function of a fuse? If they melt the plastic, they are doing exactly the opposite of what a fuse is supposed to do. This is a "fuse" problem that will be fixed with a fuse. If a fuse is installed that blows right away, then he knows to look further.
 
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mrblaine said:
How does any of that change the precise function of a fuse? If they melt the plastic, they are doing exactly the opposite of what a fuse is supposed to do. This is a "fuse" problem that will be fixed with a fuse. If a fuse is installed that blows right away, then he knows to look further.
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Because I don’t have any quality 20amp fuses I put a crap 25amp fuse in and it was fine. Does this tell you anything?

I’ll check the voltage when I get home just to see what it is.
 
JMT said:
Because I don’t have any quality 20amp fuses I put a crap 25amp fuse in and it was fine. Does this tell you anything?

I’ll check the voltage when I get home just to see what it is.
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It tells you that the crap 25 amp isn't and the quality version isn't. You aren't going to tell much difference in a compromised circuit between 20 and 25 amps. If it is shorted to ground or has a similar high draw amperage that will pop a fuse, 5 amps isn't going to matter unless you are dealing with very tiny wire.
 
Voltage on Fuse #1 is 12.48 non-switched power. The rest of the fuses are the same whether switched or non-switched. I’ll get a good fuse and report back.
 
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JMT said:
Not sure how to fix the tension in the fuse holder.
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Use a pick to bend the connector closed? Remove the wires out the back of the block and use pliers to crimp it tighter?

(Not saying this is your issue,just addressing this question)
 
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Rickyd said:
Use a pick to bend the connector closed? Remove the wires out the back of the block and use pliers to crimp it tighter?

(Not saying this is your issue,just addressing this question)
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I’ll try the pick. I can’t get to the back of the block. I could pull on it some more and see what happens! 😆
 
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Show us what you are installing into the fuse holder,
and show me the fuse holder.

Im an electrical worker by trade (AC transmission/ distribution) and Ive rewired entire vehicles in racing.(DC)

No fuse should melt like that unless its a defective unit, or its NOT a fuse and theres a short. Its a protection device that SHOULD blow if the amperage is exceeded. The fact you had 2 back to back glowing makes me think youre not using actual or good fuses, and youre closing the circuit with an overload (short)

Even a piece of metal can close a circuit to get it working, but if a short occurs there is no protection and the wires will overheat til sheathing failure (in this case a nonfunctional fuse melts) and cause further shorts along the circuit

FYI They also sell mini DC circuit breakers for troubleshooting circuits. Never ever put a higher amp rated fuse in a circuit with a lower rating

Youtube has videos on chasing these
 
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A direct short will blow a fuse. A melting fuse may mean a build up of resistance which is enough to create heat but not enough to blow the fuse. I would start at the terminal and look for looseness or corrosion. A failing solder joint or cracked circuit board is also a possibility. The resistance could be farther down the circuit. Are the wires hot? Get an infrared thermometer and start checking along the circuits.
 
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bucky said:
A direct short will blow a fuse. A melting fuse may mean a build up of resistance which is enough to create heat but not enough to blow the fuse. I would start at the terminal and look for looseness or corrosion. A failing solder joint or cracked circuit board is also a possibility. The resistance could be farther down the circuit. Are the wires hot? Get an infrared thermometer and start checking along the circuits.
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That’s my understanding, a build up of resistance. I’ll look into your other suggestions too. I can check wire hotness.
 
I’ve only ever used ones from auto parts stores. Usually Bussman, I think.

I think some stores sell a brand called Littelfuse, but I don’t recall ever using them.
 
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mrblaine said:
As a test, when you get some good fuses, give each tab a little twist to tighten that up in the fuse block and see what happens.
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I tried a different type of fuse. No idea what it was. It was fine when the key was off. When I turned the key on I immediately heard it fry. It did not heat up like the others. The only difference is my instrument cluster is not hooked up and I twisted the spades. I need to collect more data.
 
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Direct short one of those suspect fuses to your battery. It should blow in less than 0.2 seconds. If it doesn’t, there is your problem. There are some total junk fuses in a clear box from amazon that the whole world is selling. Direct shorting your battery is a really bad idea in most cases, obviously. Unhook your negative and just short it for a split second. That won’t hurt anything.

That fuse is there to prevent other stuff from melting and catching fire. The fact that the fuse melted means other wires in that circuit probably suffered the same fate.
 
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