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.

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Story Summary Overview

  • Similar to a fuse, a fusible link serves to protect the rest of the electrical system from excessively high current loads
  • Too much current (amps) will cause the fusible link to fail, cutting power to more expensive components downstream in the electrical circuit
  • Fusible links can be cheaper and easier to install than a replaceable fuse
  • Generally, a fusible link’s wire is four gauges higher (smaller) than the rest of the circuit, making it the weakest link in your electrical chain
  • A fusible link can be tested with a multimeter

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

anl and maxi high-current electrical fuses on a workbench
Fusible links have been replaced in many modern applications with the advent of high-current ANL and “Maxi” fuses. In some situations, you may even find a resettable breaker instead. (Image/Jefferson Bryant)

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.

We have an in-depth article on fuses here: All About Vehicle Electrical Fuses

How Does a Fusible Link Work?

pico fusible link horizontal
(Image/Pico Wiring)

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.

Where Will You Find a Fusible Link in a Vehicle?

Wiring Harness with Fusible Link
Fusible links are often integrated directly into the wiring harness, particularly in high current circuits like your starting and charging systems. (Image/Summit Racing – Mike Norcia)

Generally speaking, you’ll find fusible links in the parts of a car or truck’s electrical system that see the most current draw (measured in amps). For a vehicle, that usually means the starting system, where battery power is sent via a larger (lower) gauge wire to the engine’s starter motor. A stuck, cold, or damaged engine may put excessive strain on the starter motor, which can result in a higher than normal amp draw—hence why a fusible link is often found here.

If you’ve ever had to crank-over an engine by hand, you know that the cylinder compression means it often requires a lot of strength to move the rotating assembly—in other words, a starter motor demands a lot of current to make enough oomph so the the engine can turn over.

Another location where you may find a fusible link is in the vehicle’s charging system, near the alternator (or generator, if so equipped). Again, this is an area of your electrical system that often sees large amounts of amperage (current), so a fusible link is often used to prevent excessive current draw from damaging your battery or alternator.

What Does a Fusible Link Look Like?

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/Pico Wiring)

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.

Understanding Wire Gauge Size & Power Demand

We’ve alluded it before, but it’s worth repeating simply because it’s a bit counter intuitive: The higher the gauge, the smaller the wire, and the less current it can handle.

Here’s a handy chart that can help.

Wire Gauge to Wire Diameter Comparison Chart

Wire Gauge
(AWG)		Wire Diameter
(Inches)
4-00.460
3-00.409
2-00.364
00.329
10.289
60.162
80.128
100.101
120.081
140.064
160.050

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.

testing continuity with a multimeter
We’re doing a basic test for continuity here. Note our multimeter has an audible tone alarm (circled in yellow here) that lets us know the circuit is good with a reassuring beep. (Image/OnAllCylinders)

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.

Learn how to do these tests in this short tutorial: 3 Basic Electrical Multimeter Functions That Every Home Mechanic Should Know

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

using a heat gun to shrink the sleeve of a heat shrink tube around a completed lineman splice
Using heat shrink sleeves on your soldered or crimped electrical connections is vital, as it helps keep rain and moisture out to prevent corrosion. (Image/OnAllCylinders)

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.

And we also have a nice walkthrough on how to make clean soldered electrical connections here: The Lineman’s Splice—How to Make Reliable Electrical Connections

Alternatives to a Fusible Link

fuse block mounted on a jeep fender
A supplemental fuse block is a no brainer when it comes to adding extra electrical accessories like a fancy stereo system with extra amplifiers, or in this case, off-roading gear like auxiliary lights and a winch. (Image/OnAllCylinders)

Nowadays, many companies offer standalone fuse blocks that allow you to run several separate and fused circuits to vital electrical accessories. Keeping your fuses in a single spot like this can unclutter your engine bay, and make service and fuse replacement a lot easier in the future.

You could also opt for individual in-line fuse holders for single circuit applications too.

A Final Caution on Replacing a Fusible Link

A fusible link is a vital safeguard against catastrophic electrical damage resulting from excessive amp loads in your vehicle. So don’t fret if yours goes bad—often times, it means that the fusible link did its job and sacrificed itself to save more expensive and sensitive electrical components downstream.

But that also means that you should FIGURE OUT WHY IT FAILED IN THE FIRST PLACE!

Simply replacing a fusible link isn’t good enough. You should determine why it blew, elsewise it could fail again soon—potentially leaving you stranded or, worse yet, damaging more costly parts of your electrical system.

It could be due to age, corrosion, or a failing component downstream—like a bad starter that’s pulling too much current, or internal engine damage that’s making the starter work harder than normal.

Once you figure out why it went bad, replacing a fusible link is fairly easy to replace and, if done correctly, should give you years of trouble-free service.

Keywords
electrical , Fuse , Fusible Link
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Author: Paul Sakalas

Paul is the editor of OnAllCylinders. When he's not writing, you'll probably find him fixing oil leaks in a Jeep CJ-5 or roof leaks in an old Corvette ragtop. Thanks to a penchant for vintage Honda motorcycles, he spends the rest of his time fiddling with carburetors and cleaning chain lube off his left pant leg.