Hook the orange wire to something in your car that gets either +12V or gets a ground when your headlights are turned on. That way it dims the display from a high default setting that you might use during the day to a level that is lower to use at night. Chose in the scanner menu whether you are hooked to a +12V or ground setup. Should be able to find something under the dash that gets powered up with the parking light switch position like a light over your ashtray or backlighting for heater controls.
Set Backlight you can also change the intensity by pressing 'VOL' to toggle your desired level to Off, High, Middle, or Low. Set the dimmer to Auto if you are going to hard-wire your scanner inside your vehicle.
Scroll to 'Set Backlight' and press E/.
Scroll to 'Set Dimmer' press E/.
Scroll to 1 of 2 options and press E/.
(For vehicle use) Scroll to 'Auto' and press E/.
Scroll to 1 of 2 options and press E/ to save and exit.
'+ Polarity' - if the orange wire gets 12V when you turn on the headlights.
'- Polarity' - if the orange wire is switched to chassis ground when you turn on the headlights.
(For non-vehicle use) Scroll to 'Manual' and press E/.
Scroll to 'High', 'Middle', 'Low', or 'Off' and press E/ to save and exit.
Scroll to 'Set Color' and press E/.
Scroll to Off, Blue, Red, Magenta, Green, Cyan, Yellow, or White and press E/ to save and exit.
Press MENU to return.
http://marksscanners.com/996xt/996xt.shtml#backlight
