What Is an Add-a-Circuit Fuse Tap and How Does It Work?
Adding a dash cam, GPS tracker or USB charger means finding a safe source of power. An add-a-circuit fuse tap (also called an add-a-fuse) plugs into a compatible blade-fuse position in your fuse box and gives you a second fused circuit for your accessory, with no cutting or splicing of the factory wiring.
Important: This is general information, not vehicle-specific advice. Always follow the vehicle and accessory manufacturers' instructions, and use a qualified auto electrician if you're unsure.
How it works
The tap has two fuse slots and a wire lead.
- One fuse keeps protecting the original circuit, at its original rating.
- The second fuse protects your new accessory.
- The lead carries power to the accessory.
What can you power with one?
Fuse taps suit low-current accessories such as:
- Dash cams and GPS trackers
- Small USB charging sockets
- Gauges and small LED lights
- Relay trigger wires and UHF ignition-sense wires
Compressors, driving lights, inverters and amplifiers need their own fused cabling and usually a relay.
Choose the right fuse type
The tap has to match the fuse already in your vehicle. Similar-looking blade fuses aren't interchangeable.
| Tap type | Fits | Approx. width |
|---|---|---|
| Mini Blade | Mini blade fuses | About 11 mm |
| Standard ATS Blade | Standard ATS/ATO blade fuses | About 19 mm |
Tip: Many newer vehicles use low-profile mini, Micro2 or Micro3 fuses, which can look like Mini blades but aren't the same. Pull the fuse out and compare it before you buy.
Both VES styles come in single, 5 and 10 packs, handy for workshops and fleet fit-outs. You can also grab a fuse grab kit for spare blade fuses.
Switched or constant power?
live with the ignition. Best for USB chargers and gauges.
live with the ignition off. Some dash cams use it for parking mode, but they need low-voltage battery protection.
Don't trust the fuse-box label alone. Check with a multimeter or LED test light.
Picking a fuse-box position
Avoid safety-critical circuits like airbags, ABS, engine management and steering. A good position:
- Matches your tap type and has room for the cover
- Gives the power type you need (switched or constant)
- Can handle the combined load of the original circuit plus your accessory
An unused slot isn't always a live circuit, so test it first.
Fuse ratings and orientation
- Keep the original fuse at its specified rating.
- Use the accessory maker's recommended fuse for the new circuit. A bigger fuse doesn't give "extra power", it just allows unsafe current. If no rating is given, ask the supplier or an auto electrician.
- Fit the tap the right way round. The tap's common input must connect to the supply side of the fuse position. Find the live terminal with the fuse removed, then test the original circuit and the accessory separately once it's fitted.
Common mistakes
Quick checklist
Tap matches your fuse type
Circuit is suitable and non-critical
You know if it's switched or constant
Original fuse unchanged, accessory fuse correctly rated
Tap orientation, connection and earth checked
Lead kept clear of heat, sharp edges and moving parts
Shop VES Add-A-Circuit Fuse Taps
Browse the full VES Add-A-Circuit Fuse Taps & Holders collection, with Mini and Standard ATS Blade options in single and multi-packs. For bigger jobs, VES also stocks fuse blocks, cable and USB chargers.