How To Inspect and Replace Automotive Fuses

During the course of ownership, there's a chance one of the fuses in your car, truck or SUV will blow out. When that happens, the results don't usually create a crisis, but it means that something on the vehicle is no longer working.

Most likely, the thing that'll quit working on your vehicle will be relatively minor. For example, it could be the backup lights, the turn signals, the high-speed setting in the climate control system's fan, the radio, or even the interior lights. Whatever the case, if a fuse blows, the device in question won't work.

For exterior or interior lighting, the possibility of a fuse being the cause of malfunction is quite likely. In fact, for any single item or system in the vehicle, the chances of a fuse being the cause of an electrical failure is high enough that, in most cases, it should be the first thing you check.

"But I don't know how to check fuses," you might say. After reading our little primer on fuse inspection and replacement, you'll know how. Relax. It's easy and you'll get a real sense of satisfaction knowing you were able to troubleshoot a little nit like this without having to go through the hassle and expense of going to the dealership.

In general, most vehicles on the road have two types of fuses. Older cars have glass, cylinder-shaped fuses with stainless steel on the ends and glass in the middle. Most newer cars have a different style of fuse that uses a plastic housing with the fusible link encased in the housing.

The accompanying photos show the latter type of plastic fuse, a typical fuse box they're housed in and how to determine if the fuse in question is blown. For reference purposes, these photos show fuses and the fuse box from our long-term Ford Focus. In the Focus, the box is located behind a cover, underneath the dash, below and to the left of the steering wheel.

As part of a little five-minute research mission we also determined that our BMW 328i, Volkswagen Passat and Ford Focus long-term cars all use the identical type of plastic fuses shown in these photos. We also checked our '99 GMC Sierra pickup and it uses very similar plastic fuses, which are a bit smaller.

If a device or system on your vehicle isn't working and you suspect a fuse might be the culprit, the first step is to look in your owner's manual. The manual will help you locate the fuse box and tell you how to access it. On older cars, the box was usually located underneath the dash to the left of the brake pedal or near the parking brake pedal. There was no cover for it, but it was still a major hassle to view because of the bizarre angle you had to place your head at to actually eyeball the box.

Most new cars, such as the Focus, have a cover that that can be removed with your hand. Or, in the case of our Passat, with a small flat-blade screwdriver. The 328i has a trick setup where the fuse box is hinged and drops down into the open glove box. The Passat, the BMW and the Sierra even come with little pairs of tweezers to facilitate fuse removal. Such is not the case with our Focus.

Once you've located the fuse box, you have to determine which fuse needs to be removed for inspection. Again, your owner's manual will help you do that. Say, for example, the backup lights don't work. Our Focus owner's manual provides a numerical chart to explain which fuses correspond with which device or system. In the case of the Focus, the backup lights are fuse 39, which is the one we show being removed in the photos.

As noted, some cars provide a pair of tweezers to help you remove a fuse. If your car doesn't have this nifty little feature, you're not out of luck. We were able to remove fuse 39 in our Focus with our hand. But in most cases, you'll need a small pair of needle-nose or standard pliers to get the fuse out of the box.

Once the fuse is singled out and removed, you need to determine if it's blown. This is usually quite easy. For the older glass fuses as well as the new plastic ones like shown here, if the metal link inside the fuse is separated, the fuse is toast. If not, then it's still good and can be reinstalled. The diagram here (straight from our Focus owner's manual) shows the difference between a good fuse and blown one.

If the fuse is blown, the next step is finding a proper replacement. Some cars come with a supply of spares; otherwise you'll need to make a quick trip to the auto parts store. The most critical element to replacing a fuse is using the exact same amperage rating as the blown one. If you use a fuse with different amperage rating, you risk either blowing the fuse again, or damaging the equipment the fuse is designed to protect.

The idea behind a fuse is that it's supposed to blow if there's a surge or short in the device or system's electrical wiring. For example, if it's a 10-amp fuse that needs replacing and you replace it with only a 5-amp fuse, the smaller fuse will blow much sooner than it needs to. Conversely, if you replace that 10-amp fuse with a 20-amp unit, it's possible you'll damage the part or system before the fuse has a chance to break and save the component.

So, once you determine the fuse is blown and procure a suitable replacement, it's time to reinstall the new one. This is the easiest part. With the new plastic fuses, they plug right back into the fuse box and usually fit into place with a little pressure from your fingers.

With older glass fuses, the installation process is a bit tougher, as they are installed by pressing one end at a time. We'll also note that with the glass fuses, different amperage ratings sometimes come in different lengths, so the right amperage rating is not only crucial from an electrical standpoint, but from a sizing one, too.

Take a look at the photos and brief captions and you'll soon be on your way to having those backup lights, or whatever electrical component has failed, working once again.