Once you have your fuse tap, the only tools you really need to connect the car radio to the fuse box are a wire crimper tool and a utility knife. If you are installing the Multimedia Player / GPS / Step down converter / LED lighting / Voltmeter / controller in a vehicle. Of course, you will also need a fuse rated with an amperage value rated for your car ICE. You should be able to find the recommended amperage rating for the fuse in the radio installation guide.
Most low-powered ICE / GPS / Stepdown converter can use a 20-amp fuse without any issues, of course also can replace to lower Ampere fuse such as 5/7.5/10/15-amp depends on device. However, for high-powered ICE with high power power-amplifier or multi power-amplifier, then this method not recommended.
Sometime It’s common to see people wire radios to the fuse box by inserting the power wire directly into a fuse slot and then inserting a fuse on top of it. Although this may work, it is also dangerous and could damage your new ICE or create a potential fire hazard. You should also avoid using a fuse with a higher amperage rating than that specified for your new ICE or stepdown converter, LED lighting.