From the 996T Manual: (
http://www.uniden.com/pdf/BCD996Tom.pdf) PG 35.
5. Before inserting the scanner in the sleeve, attach the cable from the previously
mounted antenna. Attach the DC Power leads. RED goes to a positive (+)
connection on your fuse block while BLACK connects to the vehicle’s chassis
ground (-).
6. Connect the ORANGE lead to one side of the headlamp switch so that when
you activate the headlights, the scanners LCD backlight dimmer level changes
color and intensity. Be sure all the connections are routed away from any
potentially pinching or slicing sheet metal.
I couldn't find the info for the XT though. Sorry. I would guess (but not guarantee) that the install would be the same.
-Joe