You want the radar detector to come on when you turn your head lights on? It would just be a matter of hard wiring it to the correct circuit.
just a disclaimer: Please don't go cutting into your electrical system unless you have a basic knowledge of what you are doing.
'14 Tuxedo Black ST3
'13 Ingot Silver Escape Titanium AWD
'04 CD Silver SVT, #877, 1 of 135 May 2011 ROTM, FF11: Best Display, Best of Show; AFN12: Best SVT, Best Audio, Finest Five, Carlisle Nifty Fifty