That's the same as putting both into the same crimp. One fuse replaces the one you removed to install the add-a-fuse; the other fuse (the one you have going to the radar detector) also goes to the new wire.
sonoronos did exactly the same thing I did - add a fuse box under the floor - I actually added two - one switched and one unswitched. The diagram is up on this thread.
What you are drawing will work as long as you don't have a problem with one of the devices that blows the fuse.
Originally Posted by XLR8BYU
Good thinking. I would definitely not want to start messing up fuses by overloading them. So, rather than crimping both wires to the add-a-circuit, how about this:
