The [99 + Enter “Setup?” Function], described in section 4.4 of the D1260 Installation Guide, is no longer available in GV2 or newer control panels.
Brightness and contrast settings are no longer adjustable in GV2 and higher control panels. Use [Command] +  and select Bright Display or Dim Display to affect the backlighting.
Selecting Dim Display turns off backlighting for the keypad display and buttons when the control panel is idle. The keypad backlighting turns on only when a keypad button is pressed or an event is active in the control panel. After approximately 20 seconds of inactivity the backlighting will turn off.
Selecting Bright Display turns backlighting on for the keypad display and buttons at all times regardless of button presses or control panel events.