What a fuse tap is and why you'd use one
A fuse tap is a small plastic connector that lets you draw power from an existing fuse in your car's fuse box without removing the original fuse. Instead of splicing wires or running new circuits, you insert the fuse tap into the fuse slot, then plug your original fuse back into the tap. The tap has a second outlet where you can connect a new wire to power an accessory — a dashcam, radar detector, USB charger, or other low-power device.
The main reason to use one is simplicity. Running a dedicated wire from your battery to a new device means finding a path through your firewall, securing it against heat and moving parts, and protecting it with a proper fuse holder. A fuse tap does the same job of protecting your new circuit — it uses the existing fuse as your protection — but takes minutes instead of hours. The trade-off is that your new device shares the fuse with whatever else was already on that circuit, so you need to pick a circuit with enough spare capacity.
Key Takeaways
- A fuse tap plugs into an existing fuse slot and lets you draw power for a new device without removing the original fuse.
- You must choose a fuse that powers something you use less often than your new device, or one with spare capacity, so the shared fuse doesn't trip.
- The fuse tap itself costs $5 to $15, and you'll need a wire gauge that matches the fuse amperage — typically 18 AWG for 10-amp fuses or smaller.
- Most cars have the fuse box under the dashboard on the driver's side or under the hood; your owner's manual shows the exact location and what each fuse powers.
- If the fuse blows repeatedly after you install the tap, the circuit is overloaded and you need to choose a different fuse or run a dedicated circuit instead.
Finding the right fuse to tap into
The first step is choosing which fuse to use. Open your owner's manual and locate the fuse box diagram — it lists every fuse, its amperage, and what it powers. You're looking for a circuit that either powers something you rarely use, or one with enough spare capacity that adding your device won't overload it.
For example, if you want to power a dashcam that draws 0.5 amps, and you find a 15-amp fuse that powers the cigarette lighter (which you never use), that's a good choice. The dashcam uses less than 1% of the fuse's capacity. But if you tap into the headlight fuse, which already runs near its limit, adding even a small device could cause the fuse to blow every time you turn on the lights.
Check your device's power requirements — usually listed as watts or amps on the charger or in the manual. If it says 12 watts at 12 volts, divide watts by volts: 12 ÷ 12 = 1 amp. Add a safety margin of 20% and look for a fuse with at least that much unused capacity. When in doubt, ask in a car forum specific to your model — owners know which circuits have spare room.
Choosing the right wire gauge and fuse tap size
Wire gauge matters because thin wire can overheat if too much current flows through it. The fuse protects the wire, so your wire must be rated for the fuse amperage or lower. A 10-amp fuse needs 18 AWG wire or thicker. A 15-amp fuse needs 16 AWG or thicker. A 20-amp fuse needs 14 AWG or thicker. If you're not sure, use the next size up — thicker wire is always safer.
Fuse taps come in two main styles. The most common is the add-a-circuit or piggyback fuse tap, which looks like a small plastic block with two fuse slots stacked vertically. You remove your original fuse, insert it into the bottom slot of the tap, then insert the tap (with your fuse inside) back into the fuse box. The top slot is where you insert a new fuse for your device. The second style is the in-line fuse tap, which has a wire already attached; you insert it into the fuse slot and the wire hangs out of the fuse box. In-line taps are faster but less flexible if you need to move the wire later.
Buy a fuse tap rated for the same amperage as the fuse you're tapping into. If you're using a 15-amp fuse, buy a 15-amp fuse tap. They cost between $5 and $15 at auto parts stores or online.
The step-by-step installation process
Start with the car off and the keys out of the ignition. Locate your fuse box — check your owner's manual for the exact spot. Most cars have one under the dashboard on the driver's side and another under the hood. Open the cover; it usually pops off or unscrews.
Find the fuse you've chosen using the diagram on the inside of the fuse box cover or in your manual. Use a fuse puller (a small plastic tool often clipped inside the fuse box cover) or needle-nose pliers to gently pull the fuse straight out. Don't twist it — pull straight toward you.
Insert that fuse into the bottom slot of your fuse tap. Then insert the fuse tap (with your original fuse inside) back into the fuse slot, pushing straight in until it clicks. The tap should sit flush with the other fuses. Insert a new fuse of the same amperage into the top slot of the tap — this fuse will protect your new device's circuit.
Strip about 1/4 inch of insulation from the end of your wire, insert it into the wire terminal on the fuse tap (usually a small metal clip), and tighten the terminal screw with a screwdriver. Run the wire to your device, find it away from heat sources and moving parts with zip ties or clips, and connect it to your device's power input. Close the fuse box cover and test your device with the car running.
What to do if the fuse keeps blowing
If the fuse blows when ready or within a few minutes of turning on your device, the circuit is overloaded. Turn off the device, remove the fuse tap, and reinstall your original fuse. The circuit you chose doesn't have enough spare capacity, or your device draws more power than you thought.
Check your device's power draw again — look at the charger label or the manual. If it's higher than you calculated, you need a fuse with more capacity. If you've already chosen the highest-amperage fuse available, or if tapping into a different fuse still causes blowouts, your device needs a dedicated circuit run directly from the battery with its own fuse holder. This is more work but guarantees the device gets all the power it needs without affecting other systems.
If the fuse blows only sometimes — for example, when the headlights and your device are both on — the circuit is marginal. You can try a slightly higher-amperage fuse if one is available, but the safest move is a dedicated circuit. Repeated blown fuses mean the wire is working too hard and could overheat.
Safety considerations and when not to use a fuse tap
A fuse tap is safe when you match the wire gauge to the fuse, choose a circuit with spare capacity, and don't overload it. But there are situations where a fuse tap is the wrong tool.
Don't tap into a fuse that powers a safety system — airbags, ABS brakes, stability control. These systems need their full fuse capacity at all times, and sharing the fuse could delay their response in an emergency. Don't tap into the fuse for your car's computer or engine control module. Don't use a fuse tap for a high-power device like a power inverter, electric cooler, or auxiliary lighting system; these need dedicated circuits.
If you're not comfortable working in the fuse box, or if you're unsure which fuse to choose, have a mechanic or car audio shop do it. The cost is usually $50 to $100 and buys you the confidence that it's done safely.
Frequently Asked Questions
Can I use a fuse tap for multiple devices?
Technically yes — some fuse taps have two wire terminals so you can power two devices from one fuse. But this increases the risk of overload. Each device adds to the total current draw. If you have two devices, calculate their combined power draw and make sure the fuse has enough spare capacity for both. If not, use two separate fuse taps on two different circuits.
What if I can't find a good fuse to tap into?
If every fuse is already at or near capacity, you need a dedicated circuit. This means running a wire from the positive terminal of your battery through a fuse holder (mounted near the battery) to your device, and running a ground wire from your device to a bare metal point on the car's frame. It's more involved but guarantees your device gets clean, protected power without affecting other systems.
Will a fuse tap damage my car's electrical system?
No, as long as you use the correct wire gauge and choose a fuse with spare capacity. The fuse tap is just a connector — it doesn't change how electricity flows. The fuse still protects the circuit the same way it did before. The risk is only if you overload the circuit, which would blow the fuse (a good thing — it's doing its job).
Can I leave a fuse tap installed if I remove the device?
Yes. The fuse tap with an empty wire terminal is harmless. If you plan to remove the device permanently, you can also remove the fuse tap and reinstall your original fuse directly in the fuse slot. Either way is fine.