On the Take Off panel there's a rotary called PNL. Assign it to 'Assign to Axis' in the backlit settings. Do this for both panels...except when you are in the Backlit settings of the Combat Panel, assign the backlit setting to the TO panel PNL rotary.
I hope this is clear.......simply you are turning your lights on or off on both panels using the PNL rotary on the Takeoff panel