Car Fuses and Fusible Links Explained

Blowing the Lid Off Car Fuses and Fusible Links

car fuse colors
Car fuse colors indicate the amperage they can handle, but they are also printed with an amperage rating. Gary Gladstone / Stockbyte / Getty

Automotive fuses are the gatekeepers and bodyguards of the automotive electronics world. Whenever a sudden short or surge threatens any of the delicate electronics found in modern cars and trucks, a fuse stands ready to valiantly throw itself into the field of fire. In doing so, the fuse takes a figurative bullet for some more valuable, complex, or indispensable component or device, like a car stereo or amplifier.

This often results in some temporary loss of functionality, but fuses are cheap, and usually easy to replace, and any underlying problem will typically be revealed by repeated failures of a fuse on the same circuit. Fusible links, while different in design, are identical in purpose and functionality.

Are All Car Fuses the Same?

Modern car fuses are all based on the standard ATO and ATC “blade type” fuses that Littelfuse patented in the 1970s. There are multiple sizes and configurations of blade fuses today, but they all bear a physical resemblance to the original ATO fuses, and some applications still use standard ATO and ATC fuses. The differences between these various types of blade fuses are primarily size and number of terminals, although physically larger fuses are usually used in higher current applications.

Older vehicles used a variety of different types of fuses, although the most common were “glass tube” fuses and “Bosch type” fuses, which can still be found today in older vehicles that are still on the road.

Glass tube fuses consist of a glass tube, capped by metal terminals, and with a metal strip passing through the center. Bosch type fuses are also roughly cylindrical, but they are made of a solid ceramic material with a metal strip on the surface.

Since automotive fuses are differentiated both by design type and current rating, all fuses most emphatically are not the same.

Although it is definitely possible to replace any ATO fuse with any other ATO fuse, doing so can be extremely dangerous if the wrong amperage fuse is substituted. Similarly, it is sometimes physically possible to replace a Bosch type fuse with an American-style glass tube type, but sticking to the same amperage rating is imperative, and a flat-capped glass tube fuse will typically not fit well into a fuse holder designed for conical end caps.

Types of Blade Fuses

There are six types of blade fuses that you may run into when you pop open the fuse box on a modern car or truck: micro2, micro3, low-profile, mini, regular and maxi. The regular type was the first one to arrive, and all the other ones are based on that basic design, with metal blades embedded in a plastic housing. The housing is typically clear, which allows for easy inspection of the fuse element, which typically comes in the form of a winding metal strip that connects the two terminals. If the strip is broken, that means the fuse has blown.

Micro2 fuses are the smallest type of blade fuse, and they are easily identifiable by the fact that they are so much taller than they are wide. In terms of size, low-profile mini fuses and regular mini fuses share the same body height and width, but the spade terminals of low-profile mini fuses barely extend past the bottom of the body.

Micro3 fuses are larger than Micro2, low-profile, or mini fuses, but they are most easily identifiable by the fact that they utilize three spade terminals. Every other type of blade fuse only uses two terminals. They also include two fuse elements, which allows a single fuse to effectively handle two circuits.

ATO and ATC fuses, or “regular” blade fuses, are the original and also the second largest type. Although many applications started to replace ATO and ATC fuses with mini fuses in the 1990s, they are still widespread. These fuses are wider than they are tall, and they come in two main types.

ATO fuses are open at the bottom, while ATC fuses feature a plastic body that is totally enclosed.

The largest type of blade-style fuse is the maxi fuse. These are significantly larger than any other type of blade or spade automotive fuse, and they are typically used for higher current applications.

Automotive Fuse Color Coding

While it’s possible to replace any ATC fuse with any other ATC fuse, any mini fuse with any other mini fuse, and so on, doing so is not safe if you don’t match the current ratings. Although fuses can blow under normal operating conditions, due to age and wear, a blown fuse often indicates a deeper problem. So if you replace a blown fuse with another fuse with a higher amperage rating, you may prevent the fuse from blowing again immediately, but you also risk damaging some other electrical component, or even starting a fire.

There are three different ways to tell the amperage of a blade-type fuse. The first is to look at the top of the fuse, where you will find the amperage rating printed on or stamped into the plastic. If the rating has worn off, you can also look at the color of the fuse body or check the fuse diagram to see what type of fuse belongs in that particular slot.

Colors and physical dimensions for blade type fuses are laid out in DIN 72581, and not all colors or amperage ratings are available in all sizes.

 

Color

Current

Micro2

Mini

Regular

Maxi

Dark blue

0.5 A

No

No

Yes

No

Black

1 A

No

No

Yes

No

Gray

2 A

No

Yes

Yes

No

Violet

3 A

No

Yes

Yes

No

Pink

4 A

No

Yes

Yes

No

Tan

5 A

Yes

Yes

Yes

No

Brown

7.5 A

Yes

Yes

Yes

No

Red

10 A

Yes

Yes

Yes

No

Blue

15 A

Yes

Yes

Yes

No

Yellow

20 A

Yes

Yes

Yes

Yes

Clear

25 A

Yes

Yes

Yes

Gray

Green

30 A

Yes

Yes

Yes

Yes

Blue-green

35 A

No

Yes

Yes

Brown

Orange

40 A

No

Yes

Yes

Yes

Red

50 A

No

No

No

Yes

Blue

60 A

No

No

No

Yes

Amber/tan

70 A

No

No

No

Yes

Clear

80 A

No

No

No

Yes

Violet

100 A

No

No

No

Yes

Purple

120 A

No

No

No

Yes

 

While color coding is standard almost across the board for different types of automotive blade fuses, two notable exceptions are 25 A and 35 A maxi fuses. These fuses are gray and brown, respectively, which are colors that are also used for lower amperage fuses. However, maxi fuses are not available in 2 A or 7.5 A, which are the ratings used by those colors, so there is no possibility of confusion.

So What About Fusible Links?

Fusible links perform the same basic function as fuses, but they go about it in a slightly different way. In automotive applications, a fusible link is a length of wire that is several gauges thinner than the wire that it is designed to protect. When all goes well, this results in the fusible link failing, and breaking the circuit, before the protected wiring can fail.

In addition to simply being thinner than the rest of the wire in a circuit, fusible links are also encased in special materials that are designed to not catch on fire when exposed to high temperatures. So while extremely high current in a regular wire may cause a fire, a blown fusible link is less likely to do so.

Fusible links can be found in a variety of places in cars and truck, but they are commonly used in high-amperage applications like starter motors, which can draw hundreds of amps. When this type of fusible link blows, the vehicle will no longer start, but the risks of fire are lessened. In other applications, the fusible link may be easier to get at and replace than the wiring it is designed to protect.

Replacing Fuses and Fusible Links

Replacing fuses is a relatively easy job that just about anyone can do, but it’s still important to take the time to make sure you replace them with the correct style and amperage rating replacement. Blade fuses are sometimes physically difficult to pull out, but most vehicles come with a fuse-puller tool that is located inside one of the fuse boxes or attached to a fuse box lid.

Although it is fairly easy for a practiced eye to identify car fuses on sight, you can also look at a visual guide to help determine which type of fuse you need to obtain.

If you replace a fuse, and you find that it blows again, that usually means there is some underlying problem that you will have to deal with. Replacing the fuse with a higher amperage fuse may seem to fix the problem temporarily, but identifying the components present on that circuit, and tracking down and fixing the actual, underlying problem, is the safer way to go.

Replacing fusible links is often a more involved job than simply pulling a fuse, since they are typically bolted in place and are sometimes difficult to reach. It is a job that you can do at home if you have the right tools and are able to physically locate the blown fusible link, but it’s even more important to replace a blown fusible link with the correct component than it is to use replacement fuses with correct amperage ratings. Since fusible links often carry tremendous amounts of current, doing the job poorly, or using just any old replacement wire, can result in a fire or a much more costly repair when other wiring fails later on.