Direct wiring a radar detector?

I keep getting a reading "low voltage" when it turns on then shuts off, I direct wired hot to the fuse box with a "piggy back" fuse, am I not getting a good ground? The radar detector works just fine in my other cars, so I know its not the problem, thanks, just for info, the car I'm wiring/hooking up is a 2015 Ford Fusion

Either the supply voltage (to the detector) is low, as the message says, or you have a defective ground. Is the ground of the detector attached to the body of the car?