Everything You Need to Know About Fuses

Everything You Need to Know About Fuses

Ever wonder where the term “short fuse” comes from? Well, you aren’t the only one. But, in the automotive dictionary, it could mean several different things. It could refer to an AGA, GMA, or ATM-style fuse. Kind of confusing, sure, but automobile fuses don’t have to be mind-boggling.

You’ll find the fuses in your vehicle’s circuit breakers, which are typically in two locations (the engine compartment and the dashboard area near the driver’s knees). What you need to know first is what kind of circuit breaker you’re looking at, then you can figure out the fuse type.

That being said, let’s discuss your fuses and circuit breakers.

Sacrificial Circuit Breakers

These fuses destroy themselves when you break the circuit. Once a specific temperature is reached, a small piece of metal in them will melt.

Glass Fuses

Glass fuses haven’t been widely used in US automobiles since 1982. There are a few different styles with different diameters and lengths. Automotive Glass (AG) fuses come in nine different styles, and SFE fuses measure 1/4-inch in diameter and between 5/8-inch and 17/16-inch in length. MDL fuses are different because they are time-delayed, meaning they burn at a slower rate.

Non-Glass (Barrel) Fuses

Bosch barrel fuses are typically found in European cars made up through the 1990s. They are similar to a AA battery and come in five different colors, which correlate with their assigned amps. The yellow, for example, is a 5-amp while the grey/black is a 40-amp.

Lucas fuses are ceramic barrel fuses that have paper labeling inside of the glass. This makes it difficult to swap them out since you cannot really see if the fuse is still good.

Blade Type

Blade-type fuses can come in a few different styles, and you can usually tell them apart with some ease.

  • Micro2: 9.1× 3.8w × 15.3h mm; fuse ratings from 5-30 amps
  • Micro3: 14.4 × 4.2 × 18.1 mm; 5-15 amps
  • Mini/ATM/APM: 10.9 × 3.6 × 16.3 mm; 2-30 amps
  • Maxi/APX: 29.2 × 8.5 × 34.3 mm; 20-120 amps
  • LP-Mini/APS/ATT: 10.9 × 3.81 × 8.73 mm; 2-30 amps
  • Standard/ATC/ATO/APR/ATS: 19.1 × 5.1 × 18.5 mm; .5-40 amps

The amperage of a classic ATC will be printed on its top and can be identified by its color. Maxi fuses are used for high-current purposes and are certainly bigger in size than the others.

Resettable Circuit Breakers

These circuit breakers can be manual or automatic. Automatics are standard while manuals are generally used in aftermarket supplies, like enhanced lighting features. Manuals are similar to sacrificial fuses but require you to just flip the button on the breaker to get things working again. If you’ve blown a fuse in an aftermarket product, you can get a manual as a cheap alternative to high-current fuses.

Replacing a Bad Fuse

Most blown fuses are easy to replace. Just make sure you’ve got the vehicle turned off before you do it. The hardest to replace is glass, bladed, and cartridge fuses since you’ll need needle-nose pliers or small tweezers to get them out. If you have a bolt-down fuse, you’ll need tools (namely a nut or socket driver).

Glass barrel fuses are highly breakable and are the hardest to remove. The glass might already be broken if the fuse has gone bad, but it can also break when you remove it. A tool that isn’t an energy conductor is required for getting them out.

These are just some of the basics about fuses in cars. While you can replace most of them by yourself with ease, you should still take all of the necessary precautions before removing the old ones.

Written by Jim Boudreau’s Automotive Service Center