On the APM 2.5 opposite side of the ABC lights is a large blue LED with a smaller red led. The blue should be solid while the red LED either blinks when disarmed or is solid if the motors are armed.
My problem is that when I plug in the battery neither the large blue or small red LED lights up.
I can get them on by unplugging the battery then plug in a USB cable into the APM wait for the blue and red LED's to come on then plug the battery in and then I can disconnect the USB cable. But no matter what when I plug the battery in first neither LEDs will come on. I have tried plugging in the USB cable while the battery is plugged in but those two lights remain off. I have to unplug everything then power up the APM with USB before plugging in the battery for those two lights to come on. Its not location either. I don't have to move the hexa around to get a lock, its in the exact same spot.
What exactly does the blue LED mean?