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HomeTips & GuidesAuto Fusible Links – How to Test and Replace It

Auto Fusible Links – How to Test and Replace It

About Auto Fusible Links: Did you know your car’s electrical components can run into power problems, resulting in damage and sometimes fires? That is why having a circuit protector like a fuse or a breaker is necessary to keep your car electrical safe. But sometimes fuses and these breakers aren’t ideal, which calls for a fusible link. Here, we discuss Auto Fusible Links, how they work, and how to test and install them correctly.

Typically, a fusible link refers to a special type of wire you install to protect your car circuit systems. It acts like a fuse that protects your car components from damage and potential fire in case of power surges.

However, it is not a fuse because you only install it where fuses are not a suitable circuit protection mode.


Your car fusible link is a short wire featuring an alloy metallic material with a low melting point. The lower melting point than normal wire ensures it melts at a certain temperature when you pass excess current through it.

In addition to the low melting point, the wire is also of small diameter to ensure a weak point in your wire. This weak point becomes susceptible to melting when you pass a current beyond the wire rating you used.

From there, your link comes with high quality insulation to contain any fire or sparks in case the wire melts. Again, the insulation protects the wiring from short circuits, contact with other components, and external factors.

You then integrate the fusible link in your harness specifically in areas prone to current surges like battery and alternator.

Lastly, they have color codes to show their current rating so you can know them easily.


As you may expect, fusible links have specifications that show their performance and where you can use them.

For instance, they have current ratings such as 10A and 20A to show the maximum current you can pass through them.

However, you should not use them at a voltage exceeding 50V and temperatures more than 150.

They also have a specific wire gauge (diameter) depending on your circuit wire gauge to determine their current capacity.

According to my research, the general rule is that your fusible link should be smaller (4 gauges higher than your harness).

For instance, if your wire gauge is 6, your fusible link should be gauge 14. Finally, your links must meet certain standards, such as SAE, depending on the application

As we established above, you connect your fusible link to any circuit that may experience high current surges. We also said your fusible link usually features a smaller diameter/higher wire gauge than your harness wire.

As you may expect, they also have current ratings, as we said above. What happens is that, in case you exceed this current rating, the link overheats and blows up, disconnecting the circuit.

It sacrifices itself so the current doesn’t pass through to destroy the rest of the wiring and connected components. When it blows up, the insulator contains the resulting sparks that might harm your systems.

While fuse and fusible link protect your circuit from overcurrent, they are different in design and application technique.

For starters, fuses are stand-alone devices you place in the fuse box while you integrate fusible links to your wiring. Again, in cars, fuses have a fixed current rating of less than 40A.

However, some devices/systems may sometimes require current surges, meaning a fuse would blow every time the current spikes. In such a case, you use a fusible link because its current rating is usually a range.

Lastly, a blown fuse is easier to replace with another, while a fusible link involves splicing the wire and installing another.

A car fuses

As mentioned above one of the main points where you use a fusible link in a car is the alternator wiring. When this fusible link goes bad, you can expect the following issues:

  • Lights are dimming.
  • Battery drain.
  • Warning lights come on. 
  • Dysfunctional speedometer needle.
  • Electrical component/circuit dysfunction.
  • Physical damage: Such as burning, blacking, melting, or destruction of the fusible link insulator.
Checking a car’s wiring

Checking a car’s wiring

Let’s see how to test and replace it.

When testing your fusible link, start by jump-starting with a wire of the same gauge as your wire harness. Connect it to the battery positive and then to the circuit that your fusible link protects. If it fails, then your fusible link has an issue. However, if it functions, your problem could be elsewhere, such as a motor or relay.

Now if your jump wire didn’t work, you must confirm the fusible link is faulty using a multimeter. You must set your multimeter to the Ohm settings to measure fusible link continuity.

First, disconnect your negative battery terminal from there to prevent power through the link. Then place one multimeter probe on the fusible link end connecting the protected device and the other on the positive battery terminal.

If it’s fine, your multimeter reading must be the same as when you connect the two multimeter probes. The reading may also have a small resistance of not more than 0.2 Ohms.

Using a multimeter

Using a multimeter

Remember, we said replacing fusible links can be a bit more demanding than replacing fuses. For this task, you will need a new fusible link of appropriate size and some tools. The tools include a soldering gun and solder, wire cutter and stripper, heat gun, wire crimps, and heat shrink tubbings.

  • Once you have the above materials, disconnect your battery negative terminal to prevent shocks. 
  • Then, cut to remove the blown fusible link from your wiring harness. 
  • From there, take the new fusible link and strip the insulator about an inch from its end.
  • When through, blend the fusible link conductor you revealed with your main wiring. 
  • Now place your crimps on this joint and solder to make it strong and sure. 
  • Lastly, insert the heat shrink tubing to cover your joint and pass a heat gun to secure it. 
  • You may now repeat the process on the other end of the fusible link and then connect your battery to test.


As a thumb rule, always use the same fusible link as the one that was there. We also established it’s mostly 4 gauge higher than your connection wire.

You may know that MAX fuses replace fusible links in older car models. But, I recommend not replacing your fusible link with them unless your car manual allows it.


My detailed research can help you to identify your faulty fusible links and replace them appropriately. 

I am Lillian Yang, having been a sales manager for over 10 years.

I have received many positive reviews from customers. They have praised our excellent service, on-time delivery, and high-quality cable assemblies.

For your projects, please provide cable assembly files/images/smples, etc., so that I can send you a quotation within 24 hours.

Contact me now and let’s get started on building your wire harnesses!

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