Arduino MEGA 2650 R3 pin 13 LED is always on, unless I connect a multi-meter
Connect 10k PUl-up resistor(Similair like on imput) to the Pin 13 in some cases internal induction on some supplies may generate enough background voltage to keep LED on
although internal capacitance may slow down blinking (dimming).







simulate this circuit &ndash; Schematic created using CircuitLab