It would be unlikely that you would overload a used slot. Plugging in one of those adaptors to an empty slot means would make it just about impossible to overload anything existing on the car.
Most modern car fuseboxes have empty spaces. Very often, a single connection goes down one side of several fuses. That single connection is often on all the time or only on when the ignition is on).
If so, you can add a fuse.
There might be a connector you can wire to on the other side of the fuse. If not, one solution is to find the correct terminal, maybe from a second-hand fusebox, and wire to that.
Actually I am planning to use a fuse holder but instead of using a used slot(and overload it) I wanted to add a fuse to an empty slot and use the fuse holder in that slot.
Is it wrong?
It would be unlikely that you would overload a used slot. Plugging in one of those adaptors to an empty slot means would make it just about impossible to overload anything existing on the car.
@rashedul Yes, you can use them, but make sure that you put the original non existent fuse in the bottom, don't put a 10A or something in since you don't know what it might power, probably nothing but it may be something that shouldn't be powered. Since that will not pass power across the fuse tap, you will need to put the fuse tap in so that the tap fuse gets it's power from the hot side of the fuse holder otherwise you wont get power.