Here is something confusing to me........ My APM2 will not arm the motors until I push the reset button.
I use a 7.4v batt through a BEC to power the board. All of my esc's are opto isolated. I run a 5800mah 4s batt for the motors. I have powered the board both ways with or without the jumper through the input and output. The only way I can arm the motors is resetting the APM2 while the batteries are plugged in either by pushing the reset button or unplugging and replugging the APM2.