with revision 1.3, the low power lcd backlight is powered by 12 volts, and controlled by an npn transistor on the ground leg. So assuming you have a 0-12v signal for the dash lights, you can break one trace on the guino and use that varying source for controlling the backlight at a high level, and still be able to adjust the brightness within that level using the guino middle button.
The low power lcd has reduced generated heat considerably. By by powering it upstream of the diode, if the power dips the unit will use the large capacitor to power the cpu (brain) and not the backlight, and thus should keep it "alive" longer. Also, I'm using 470uf caps these days.
