This is a better answer. The power that goes to those lights is always on (you can turn them on with the key off) You don’t want your radar detector to be always on.I'd run a dedicated "hot" wire from a fuse box location that is "hot" when the ignition has been switched on. I've done that on my own 2004 Frontier for the aftermarket cruise control.
Or maybe tap into the "red" wire to the stereo (the "yellow" is "always hot", for the stereo memory). Those are the universal stereo wire colors, of course Nissan may be different.