Ins and Outs of Automotive Fuses | Hagerty DIY

– Hi, I’m Matt Lewis with
Hagerty, and in today’s DIY, we’re gonna be talking
about automotive fuses: where they are, how to test
them, and what to expect. In every car, you’re gonna find fuses, and these fuses are designed to protect the electrical circuit
that they’re connected to. The way in which they do this is they are the weak link in the circuit. If something goes bad, shorts out, this is the first point of
failure in your circuit, as opposed to a wire
overheating, catching on fire, or damaging some electrical component. In order to test fuses
today, I’m gonna be using our handy dandy multimeter. For this, we’re gonna change the setting over to DC voltage at 20 volts, so one of the ways you can
test a fuse is with voltage while it’s still in the car, so I’ve hooked my bench battery
up to this fuse holder here, and we can see, with the negative terminal hooked to the negative for the battery, our output wire is at 13 volts. Now, this is a fairly
common automotive fuse. They may come in different sizes, but this particular blade style fuse also gives us two terminals
on top of the fuse. This is another area you can test the fuse without removing it from the holder, and what you would do
is take your positive and test this little spot. Again, we’re at 13.4, and you can come over here
and test this side, 13.4, and what that means is
the electricity is flowing from our battery through the
fuse and out to our lead here. This is where you would
find a light bulb or a motor or your radio hooked up. Now, if this fuse was
bad and still in the car, you may read voltage on this
side and nothing on this side, and what that means is
there’s no longer a connection between these two points in your fuse. That signifies a bad fuse. Another way you can test the fuse, if it’s not in the fuse holder, is with our ohm or continuity setting, so we’ll go ahead and switch
this over on our multimeter. Again, make sure that our
leads are hooked up correctly, and go ahead and hook one
terminal up to one side and the other terminal up to the other. Here, we can see we’re well below one ohm, which means these two terminals
are connected internally. That’s the sign of a good fuse. If this fuse was bad, it would read open, just like that, as if you weren’t connecting the two. Lastly, with a fuse like this, this plastic is translucent,
so you can actually see in to the fusible link that’s
inside of this fuse, and you can do a visual
inspection to say is this burnt? Does it look like
there’s any issues there? No, this fuse looks good, so that is a quick visual inspection if you don’t have any tools on you. Now, with automotive fuses
like this blade fuse, there’s a couple of telltale signs as to what you actually have. The color of it is going to denote what the amperage capacity of the fuse is, as well as the number 10 on top here. If your circuit exceeds 10 amp
for any given amount of time, this fuse will fail. You don’t want to move up in amperage size if your fuses start blowing. There’s another problem. You’re gonna wanna figure out
what that other problem is, so don’t go from a 10 to a
15 if you keep blowing 10s. Hunt down the problem that
you’re actually having, because the wire isn’t
designed for that circuit to be using more amperage, and it could heat up and cause issues. So, now I know we have a bad fuse, because I went ahead and blew this one just to show what it would look like, and if you do a visual
inspection between the two, you can actually see
there is no connection from side to side. It’s melted back. If we put it in our fuse holder, we can use our multimeter
again to track voltage on it, so we check this side of the circuit that our light or whatever
it would be is connected to. We have nothing. We move in and check this
top post of the fuse. This side has nothing. The other side does have voltage, and that’s because this post on the fuse is hooked directly to the battery. A bad fuse will read
voltage on the battery side, and no voltage on the load side, and like we did before, if we take it out and measure continuity
with our ohm setting. We can see there is no continuity. Our meter doesn’t change at all, measuring between the two
blades of the blade fuse. So, that means these two
are no longer connected. The fuse has failed, or functioned properly and is now dead. Alright, so now that we’ve
looked at a fuse on a bench, let’s go over to our Volkswagen
Beetle and take a look at what the fuses are in this car and test them out and see how they look. So, here we are inside
of our classic Beetle. You’ll notice these fuses
are quite a bit different than the ones I had on the bench. The bench fuse was called a blade fuse. This is a ceramic fuse. This is pretty common in
older European vehicles, to see this kind of fuse. Just like the blade fuse, you
do have a visual inspection. Is there a connection here? And you can check them the same way with your voltage setting
on your multimeter. So the first thing you’re gonna wanna do is with your ground lead, you’re
gonna wanna find somewhere to ground it on the vehicle. There’s a couple places you could look, but the chassis of the
car or the body of the car always acts as the ground,
so we have a bolt here holding up the steering column. We’ve got a bolt here
holding up the power outlet, and actually, I know that the inside of these power outlets here, the inside of these power outlets also are the ground on the outside. For the sake of making this easy, I’m just gonna hold it up
against our steering column bolt. Now, it is worth noting that these fuses may not have power all the time. This white one here is a constant fuse, meaning it always has power. This next one in, this blue one, doesn’t have any power with the key off, but if I turn our key on, now, we see it has power on the fuse, and this is what’s considered
an ignition circuit, meaning that it’s off when the car is off and it’s on while the car is on. A circuit that turns on with the key, a good example would be your radio, or say your heater, the fuel pump only wants
to run when the key is on. Those sorts of things
are under what’s called switched power or ignition power. Something that would run
under constant power, like we see with that white fuse, would maybe be your headlights. It doesn’t matter if the key’s on or off. The headlights always work. Same with your interior lights, if you have lights on
the inside of the car. You don’t wanna have to have the key on for the lights to turn on
when you open the door. Those types of circuits are
on a constant power circuit, meaning they always are
connected to the battery, regardless of where the key is. So, when you go to replace a bad fuse, make sure you match up the
current load of the fuse to the circuit that
you’re replacing it in, and then, for this kind of a vehicle, it is a spring loaded fuse, so you put one end down
and the other end up, and these are not as user
friendly as a blade fuse. You wanna get it just like that, so the bottom’s in this hole
of this spring loaded side, and the top’s in the hole
of this stationary side. If you don’t know where the
fusebox is for your car, go ahead and open your owner’s manual. It’s going to say exactly
where all the fuse boxes are located within your car. If you don’t have an owner’s manual, go ahead and look under the hood. That’s a common location for fuses, as well as under the dash like
it was in this Volkswagen. Well, I hope this simple
explanation of fuses and how to test them in
your automobile was helpful. If you have any questions or comments, please leave them below,
and hit the subscribe button so you never miss another video.

Paul Whisler


  1. You're right about the VW fuses. They are kind of finicky. Good video, guys. Keep it up. ☺

  2. Thank you for making this series of DIY videos! I would like to see some more like it including adding radios and accessory components to existing electrical circuits. There are lots of videos and tutorials out there but your content quality and explanations are great.

  3. My car from 1973 has two fuses and will run even with one. Times have changed with how many cars have now.

  4. I'm a test light on the top of fuse kind of guy, for fast trouble shooting on sketchy wiring.  I like the instant yes no of the light, then dig in with the meter after you find that thing that was spliced into the backup lights and ac compressor with a home style wire nut the previous owner wrapped in electrical tape.  Other than that great video.

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