The add-a-fuse kit (also known as fuse tap or add-a-circuit) is a popular option for dash cam installs as it can make for a much more professional looking install and offers added protection for your dash cam or hardwire kit. The add-a-fuse does exactly what the name says and adds a new fuse (Fuse #2 in the diagram below) for the new circuit going to the accessories you want to connect to your fuse box. You can use the add-a-fuse to piggy back off of an existing fuse in the vehicle or simply plug it into an empty fuse slot if that's an option on the vehicle you're installing in. The power wire for the new accessory will plug into the blue portion of the add-a-fuse and crimped in place with something like needle nose pliers or dedicated crimping tools.
There are two ways you can plug an add-a-fuse into a fuse slot since there are two fuse legs and two fuse slots, but there is a correct orientation to plug it in. To test which orientation of the add-a-fuse is correct you will need a circuit tester or multi meter. Put a fuse into the Fuse 2 slot but leave fuse 1 empty, the orientation that has power going to Fuse 2 will be the correct way to plug in the add-a-fuse. If it's plugged in this way, Fuse 2 is getting power from the fuse slot directly and it doesn't put additional load on Fuse 1 so it'll be less likely to blow Fuse 1.
Other Installation Notes
When crimping the add-a-fuse, make sure that the silver metal cylinder on the blue female end is making contact with the wire you are putting in. Those that plan on installing a Cellink B should note that an add-a-fuse is mandatory for a hardwire install. The wire gauge is much too thick to simply wrap around a fuse and plug back in to the fuse slot. With regular dash cam hardwire kits such as the BlackboxMyCar hardwire kit, Multi-Safer, or Power Magic Pro, you may find that the wire gauge is too thin for the socket on the add-a-fuse. In this case, you must use extra caution as the wire can fall out of the add-a-fuse. We recommend using electrical tape or heatshrink to keep the wire tightly inside the add-a-fuse. You can also solder this connection to prevent the wire from slipping out. If you break the blue female socket of the add-a-fuse when crimping, you can still use this kit but would need to splice the new accessory's wire into the red wire on the add-a-fuse.
For Cellink installations, we recommend using an accessory fuse of at least 15A as it has been known to blow 7.5 or 10A fuses. For regular dash cam hardwire kits you can use as low as a 2A blade fuse but if you don't have one handy it's okay to run a higher amperage fuse. Most high quality dash cam hardwire cables will have inline 2-3A glass fuses that will protect your dash cam in addition to the protection the add-a-fuse offers. Vehicles that run low-profile fuses should go with the add-a-fuse as it is very difficult just to wrap a wire around a fuse leg and plug it back in with low-profiles fuses.
If you are unsure of what fuse type your vehicle uses, feel free to send us an email as we may have experience with that particular vehicle. Furthermore, if you can send us a picture of the fuse box we can help you match it with the fuse chart above.