thanks for the reply mike;
you have the correct schematic. i swapped sensors, no change; these are normally very precise (& easy to burn up if one is half-asleep). changed one megs to 3.3meg &
unit now turns off two-three hrs after sunset. progress! oddly the LED turn-on indicator, controlled by the same signal but on a diff. quarter of the LM339 turns off at what seems to be the right time / temperature. i am wondering, as well, if the 10uf cap on the temp signal is maintaining that voltage for too long. not sure of its purpose other than a buffer, temp changes are not that fast. any other ideas will be appreciated.
ed c