How to tap into a car fuse box

What's a fuse tap do?

A fuse tap allows you to get 12 volts from your vehicle's fuse box for a low-power device, like an active signal processor, an amplifier turn-on circuit, a radar detector, or a backup camera. Because of the thin size of a fuse tap's power wire, you should only use one to power a device that will draw no more than 5 amps of current or put out no more than about 52 total watts of power.

You should not use a fuse tap to supply power for an amplifier — that would be dangerous to your vehicle's electrical wiring. An amplifier requires a thick power cable to be run from the amp directly to the battery.

How to install a fuse tap

The rest of this article will walk you through the process of installing a fuse tap. The first step is to find an appropriate circuit to tap into and make sure you have the right kind of fuse. Then install it, test it out, and button it up. Let's go.

Find the best fuse to tap

Step 1: Locate an interior fuse box that is easily accessible and will provide a direct and short path for the power wire to be run to the accessory.  Do not use a fuse box in the engine compartment, because the fuse tap won't provide a water- or heat-proof connection necessary for under-the-hood electrical wiring.

Step 2: Take the cover off the fuse box. There will be a diagram or chart of the fuses with their locations and functions labeled. Identify an appropriate fuse and circuit to tap into that will power on and off with the car.

• Good choices include the radio, an interior light, a lighter-type charger port, etc
• Avoid using circuits for the starter, airbags, sensors, unknown "alphabet soup" labels, etc
• You can use an empty fuse socket, if it powers on and off with the car. Test with a meter, if possible.

Step 3: Identify the type of fuse, so you can get the right size fuse tap and accessory fuse. The owner's manual should identify the type of fuse used in your vehicle

• Types: ATC, Low-Profile Mini, Micro2, ATM (MiniATC)
• For most applications, a 1A or 3A accessory fuse will work best. Never use an accessory fuse rated higher than 5A.

How to install the fuse tap

Step 4: Switch off the car. Remove and set aside the factory fuse.

Step 5: [Skip this step if you don't have a meter.] Turn on the car. If you have a DC volt meter, test and identify the hot (+12V) and load (0V with fuse pulled) sides of the fuse socket, and confirm that the hot voltage switches on and off with the car.

Step 6: Connect (crimp) the fuse tap wire to your new accessory device's power wire.

Step 7: With the car switched off, plug the fuse tap into the removed fuse's socket, with common side contact to the hot socket and the wire side contact to the load socket.

Step 8: Plug the appropriate fuse for the new device into the tap's accessory fuse slot.

• The accessory fuse will be wired in parallel with the factory fuse, so the factory circuit will be fused at the sum of their ratings, which could be dangerous to the wiring if the accessory fuse is too large
• For safety, use an accessory fuse that's rated much smaller than the factory fuse
• Use an accessory fuse rated for 5A or less

Test, troubleshoot, then button it up

Step 9: Switch on the car and new device.

• If there's no power or turn-on for the accessory: switch the car off, reverse the fuse tap in its socket, then turn the car back on
• If the accessory powers on: okay

Step 10: Turn off the car, and then plug the factory fuse in the proper slot of the fuse tap, if it was removed in Step 4. (Adding a fuse to a circuit that didn't originally have one could damage factory wiring.)

Step 11: Secure the new power wire in position. Close the fuse box cover.  You may have to modify the cover to allow the fuse tap and new wire to sit neatly inside without being pinched or interfered with.

Make sure you have everything

If you don't already have all the wiring hardware necessary to conveniently power-up your new device from a fuse box, give us a call or chat with us online to get everything you'll need. Crutchfield's the best place to get car audio wiring hardware like fuse taps, fuses, and hookup wire, because of the added benefits of receiving free lifetime technical support with your purchases.