How To Tap Into a Car Fuse Box
Sometimes, audio enthusiasts need to tap into the car fuse box to wire in an aftermarket product or other auto parts.
A cheap and extremely useful little device, the fuse tap will give you the neatest and most secure way of tapping into your factory electrical system and adding a circuit to a car fuse box.
It’s not as difficult as it seems, and probably the most awkward part is finding the car fuse box, getting on your hands and knees and fitting it.
But if you do need advice on how to tap into the fuse box in a car, read on…
What Is a Fuse Box in a Car?
Cars have various electrical components that need a fuse to protect against short circuits. In cars, there are two fuse boxes, one located under the hood, near the engine, while the other is located inside the car somewhere near the dashboard.
The car fuse box under the hood protects engine components such as the engine control unit (ECU), cooling fan, and the battery. Whereas the fuse box near the dashboard protects cabin components like interior lights, the car radio, or turn signals.
What Does a Fuse Tap Do?
A fuse tap allows you to tap into your car’s electric circuit and draw 12 volts from your vehicle’s fuse box for any low-powered device.
They aren’t designed to power anything that needs more than 5A of current, so don’t try and tap into your car fuse box to run an amplifier. But you can tap into the fuse box to run your remote turn on wire or other smaller car audio parts.
Tools and Parts You’ll Need
Tapping Into a Car Fuse Box with a Fuse Tap
Every car will have 2 fuse boxes: one for the engine electrics which will be under the hood and the other will usually be located in the car interior, under the dash and probably near the brake pedal. This is the fuse box we will need to tap into.
Once you locate the fuse box, the first thing you should do is look at the fuse layout diagram, which will be stuck to the fuse box access panel. This will show you where all the fuses are located in the fuse box, and you’ll get a good idea for which fuse you can tap into.
On the diagram, look for fuses that will turn on and off, such as the cigarette lighter, car radio or the accessory wire. You can also use any spare fuse port if it powers on and off.
You shouldn’t tap into the fuses that are for things like the airbag, or clock as these will have constant power circuit even when the engine is off.
In your car fuse box, identify the type of fuse needed, so you can get the right size fuse tap.
The owner’s manual should explain the type you need, but it’s usually an ATM, ATM-LP, or an ATC fuse tap. As you can see, they’re all the same thing but hold different sized fuses.
Check The Fuses with a Voltmeter
Once you locate a fuse, or spare fuse port, that you believe will be ok to tap into, you want to check it with the voltmeter to make sure the power goes on and off as you switch the car key on/off.
With the voltmeter, make sure you set it to DC, and then place the black (-) probe to a solid grounding, which can be a bolt or something that is connected to your grounding.
Then with the red (+) probe you want to stick this into the fuse that you think will be ok to tap into.
Make sure you stick the probe into the fuse with the car electrics switched off, and make sure it reads nothing. If it shows some power reading, you can’t use it as this means it will be on the constant electrical circuit.
If it reads nothing, then switch the car electrics on and stick the probe in the same fuse again. Now it should show that you have sufficient power around 12V. This shows you that there’s a current and that this fuse is good to tap into.
Next, the fuse you’re tapping into, you need to pull it out with some needle nose pliers. Now, you want to see which side of the fuse is the hot (12V) and draw (0V) sides.
Now crimp the fuse tap wire to your new device’s power wire, which should have a protector sleeve, like the blue one in the image above.
Once the wiring is secure, you’re ready to try it out, but make sure the car electrics are switched off.
The ATM/ATC fuse tap will have four holes that you’ll be able to connect two fuses to: the existing, factory fuse you’re tapping into, and your new fuse. Make sure you put the fuse in the right way around or you will blow the fuse.
Of the two fuses on your fuse tap, make sure the top fuse is a lower amperage than the bottom one. For example, if the two fuses are a 30A and 15A, then the 15A fuse should be at the top.
Once the fuse tap is secure in your car fuse box, turn on the electrics and try your new device. As long as you have followed the above instructions, you should successfully tapped into your car fuse box.
Tapping Into a Car Fuse Box
Anyone who wants to build the best car audio system will likely need to tap into the car electric system from time to time.
There are many ways to achieve this, but tapping into the car fuse box will give you the best and safest way of getting the job done.
It can be awkward if the fuse box is in a hard to see location, but with a bit of agility, it should be no problem.
Once done and done right, you will be able to run your system how you like, with no fear of anything blowing.