I have an extension cord running to a shed, providing power to a heated waterer for our chickens in the winter. (I am aware that an extension cord is not ideal! It runs on a GFCI outlet.). The cord is heavy duty, grounded, outdoor rated, and has an LED indicator in the receptacle that illuminates when it is plugged in. This light is helpful, because I can simply peek in the windows to ensure that the waterer has power and know that my chickens water will not freeze.
Here's the odd bit. When it's very cold, say -10 degrees F or lower, the indicator often fails to illuminate. I know the power is on because the water isn't frozen and the GFCI hasn't tripped. As soon as I unplug the waterer, the light come back on. While it may be temperature-related, temperature isn't the only factor otherwise the light wouldn't come on when the waterer is unplugged.
What explains this intermittent failure of the led to light up?