Tech Articles

Fusible Links: What Are They and Where Do They Go?

fusible link

This fusible link did its job. It overheated and broke the electrical connection before any critical parts could be damaged. (Image/CorvetteForum.com)

Fusible links—also spelled fuseable and fusable—serve a similar purpose to a fuse. (You can read more about fuses here.)

Just like a fuse, the link is designed to handle a lower current (amp) load than the rest of the system so, in the event of a short or overload, the link will be the first failure point. When it fails, it will break the continuity in the rest of the circuit, preventing damage to other components down the line.

A fusible link typically costs a couple of bucks and can be replaced in 30 minutes. A starter motor or ECU? Not so much.

But fusible links look much different than fuses and are used for different applications.

What’s the Difference Between a Fuse and a Fusible Link?

In an automotive context, fuses are typically used on circuits with a relatively low current draw, measured in amperes, ranging from one amp to 40 amps.

But certain automotive components require momentary higher peak current levels depending, so a fixed-rating fuse may not be ideal. Fusible links are also cheaper and easier to install than a dedicated fuse block, which is why you see them in OE applications.

How Does a Fusible Link Work?

Wire is measured in “gauge,” often abbreviated AWG for “American Wire Gauge.” The lower the number, the bigger the wire. Bigger wires handle more current (amp) draw. Check out this cable calculator chart to learn more.

Again, a fusible link’s function is very similar to a fuse. It’s designed to fail before your wiring harness melts to goo.

As a general rule, a fusible link is made of wire that is four gauges higher (smaller) than the rest of the circuit, making it the weakest link in your electrical chain. For example, a fusible link in a 10-gauge wire would be 14-gauge.

The smaller-gauge wire handles less current than the rest of the circuit, so it will overheat first and, by doing so, will break the physical connection between the wire to which it’s inserted.

What Does a Fusible Link Look Like?

Pico Fusable Link

Pico makes fusible links and is nice enough to give each one a plastic tab with the wire gauge and “fusible” written plainly to see. (Image/Summit Racing)

Well, that’s the fun part. They look like wires, which can make troubleshooting a headache—we’ll get to that in a second.

When you’re combing over your wiring harness, you’ll want to look for a short section of wire (usually a few inches long) that has a smaller diameter than the wire into which it’s connected. There’s also a good chance that the link will be a different color than the wire.

Remember, a fusible link is going to be four gauges higher (smaller) than the rest of the circuit.

If it was a factory-installed link, it will probably have a nice  jacket or boot covering the splices.

The link may be at the very end of the harness as well, ending at a ring terminal secured to a solenoid, battery, or motor.

Troubleshooting a Fusible Link

When a fusible link does its job, it will break the circuit continuity, which is akin to cutting the wire. That results in cutting off power to the component.

We see this a lot in starting systems. A fusible link will blow, and folks will incorrectly diagnose a failed starter motor—turn the ignition key…and nothing will happen.

If this (or something similar happens), you should check for blown fuses in your fuse box first. If everything looks okay, pop the hood and inspect the wiring harness for melted, scorched, or broken wires.

Don’t panic if you see one, as it may simply be the fusible link doing its job.

You can also check for electrical continuity using a multimeter‘s continuity setting. Clip a lead on one end of the circuit and the other to its opposite end. If continuity exists, then your problem is likely elsewhere.

Avoid using a simple 12-volt continuity test wand for something like this, as your circuit may not automatically have 12V present. (An upstream switch or relay may also prevent an accurate diagnosis.)

Replacing a Fusible Link

Replacing a link is as straightforward as cutting out the broken link and installing a new one.

Many fusible links now come with a crimp connector pre-installed, which simplifies the installation process.

Remember to weather-proof your connections—cover your joints with heat shrink tubing or tightly wrap your connections with electrical tape.

Need a good 101 tutorial on electrical wiring? Check this out.

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19 Comments

  1. Starters don’t use fuseable links as they will draw over 300 amps.
    Fuseable link wire is nichrome so it will not solder.
    Fuseable link wire has stopped being sold in most countries now as it is a fire hazard.

    • Hey Scott–thanks for the heads up. We’ve made some adjustments to the story based on your insight.

    • Why in the world would fuseable link wire be nichrome? Nichrome has moderately high resistance, and a very high melting point. Kind of the opposite of what you want in a fuseable link. You want it to burn open in a hurry when overloaded – not to melt all the insulation off and sit there glowing cherry red.

      • Willie Smith says:

        You’re absolutely right Joe and in reference to Scott’s comment about fuseable links not being used in starting circuits my Expedition has a fuseable link between the battery and starter/solenoid +power wire

      • Exactly! Unfortunately the first users comments is inaccurate. Fusible link is copper wire, like the wiri g in the test of the system. And where did it state that “fuseable links are fire hazards”? They are not. Also, they are still sold like they always have been. Terrible info.. should be deleted.

  2. Lewis R. Bedenbaugh says:

    Glad I read Scott’s reply. I was ready to purchase a link for my starter.

  3. “Replacing a Fusible Link”
    Get a decent, marine grade, waterproof fuse holder and use that in place of the terrible, corner cutting, garbage that the factory used.

    Or let’s just keep cutting corners, doing shoddy work, and making vehicles not last so we can sell more vehicles and make more money.

    “What’s the Difference Between a Fuse and a Fusible Link?

    In an automotive context, fuses are typically used on circuits with a relatively low current draw, measured in amperes, ranging from one amp to 40 amps.

    But certain automotive components require momentary higher peak current levels depending, so a fixed-rating fuse may not be ideal.” Completely FALSE!!!

    Standard automotive fuses are what’s known as “slow blow fuses” and they behave the same way as fusible links, except they are much safer, and easier and less expensive to replace.

    And there is no limit to the available amperage of fuses.

    What would be better in a lot of applications is circuit breakers.

    • Normal automotive fuses are not slow-blow. Check the manufacture BUSS, and they can clearly show a picture of both types of fuses. In standard electronics, a slow-blow fuse may have a small resistor in the glass envelope. A slow-blow fuse is used to withstand a higher current draw during an initial start up; EX a circuit that normally draws 1 amp of current when operating, however that same circuit may initially draw 1.5 amps on start up.

      Hopefully that explains the difference between the use of a slow-blow, vrs normal fuses.

  4. Jeff Zeinert says:

    I dont have power to my fuse box located in my trunk on a 2007 volvo s80. Its module A the black box. Do you think it could have a fuseable link blown? Not sure what color wire feeds that module or where it gets its power from

  5. michael delguidice says:

    I have a 2002 nissan maxima that has a link connected directly to the positive battery terminal that appears to be blown. I tested the battery which holds 12 volts yet not enough power to keep the car running. Before i go spend a bunch of cash on something that still works id like to hear what is thought about my problem. Perhaps even put me on a trail of adventure trying to find out what is wrong

  6. larry c counts says:

    Thanks for the info i learned a little now i will fix my wiring on my 1985 c10 truck.

  7. Gary Gray says:

    QUESTION, DOES A 2010 TOYOTA TUNDRA HAVE AN INLINE Fusible links? if where would they be located… going agro!!!! please help! thank you much.

  8. Hi
    I was (am?) having trouble starting my riding mower, John Deere LT133. Brake safety switch was broken so I changed it, and I noticed a wire coming from engine block was burned out cut…cover melted and wire in it looked much more like a little metal rod. I’m guessing it is fusible wire. The mower is working: engine starts, gears engage, cutting blades engage and mows…
    So my question: Do I need to have that fusible link replaced? It seems to be working just fine with that wire burned off and not connected.
    Thank you

  9. IAM HAVING TROUBLE STARTING MY 05 CHEVY TRAILBLAZER
    AFTER REPLACING MY FUELPUMP/SENDING UNIT, WHERE IS MY OR ANY FUSABLE LINKS THAT CONTROL THIS UNIT ?

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  13. Shannon M Johnson says:

    My car battery died when it stormed one day and there was so much water on the streets that I was having to drive through it so after driving through some water off and on my lights went doom and my car cut off the battery was completely dead while going down the road I got a jump then next day battery died again I noticed my alternator belt was broke could the fuseable link blow then car keep driving to the point where the alternator belt breaks bc now im overheating when I turn on my air conditioner so could the fuseable link cause the engine to overheat when more power is used to run the air

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