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PICO-APL1 onboard LEDs and optional external LED
There are 3 LED indicators on the PICO-APL1 board.
Red LED indicates standby voltage ready
Green LED indicates operating voltage ready
Blue LED is the hard disk indicator
In addition to the LEDs on the board, the PICO-APL1 can connect external LED via front panel CN3. 
(Info from PICO-APL1 Manual)
Here is schematic of CN3
HDD_LED signal (pin 3 and 4)
PWR_LED signal (pin 7 and 8)
Both are an voltage 3.3V with 330 Ohm resistor , it pull maximal 0.01A current.