The Old Man in the Cave

Info from IMDB

In a post-apocalyptic settlement in 1974, the inhabitants' survival is dependent on the advice of an unseen man living in a nearby cave. This dependence is tested when a band of soldiers descends on their town

[Opening Narration] What you're looking at is a legacy that man left to himself. A decade previous, he pushed his buttons and, a nightmarish moment later, woke up to find that he had set the clock back a thousand years. His engines, his medicines, his science were buried in a mass tomb, covered over by the biggest gravedigger of them all: a Bomb. And this is the Earth ten years later, a fragment of what was once a whole, a remnant of what was once a race. The year is 1974, and this is the Twilight Zone.

Storyline

Ten years after an atomic apocalypse, a small group of survivors manage to eke out a very difficult existence. They've managed to survive in large part due to the advice they receive from an old man who lives in a cave outside of the town. Goldsmith acts as the intermediary and the old man's advice on things like crops or the safety of a batch of old canned goods are usually correct. When four soldiers led by Major French arrive in the town, the social order is upended with the townsfolk attacking the old man's cave but not really prepared for what they find inside. (Written by Gary KMCD).

*****

These rough soldiers dispute the idea that Goldsmith receives wisdom from someone in a cave which turns out to be a computer which was in use prior to the nuclear holocaust. Indeed, it turns out that people would rather destroy a valuable source of information than broaden their minds to entertain the idea that humanity has devolved from a greater technological civilisation (Atlantis) or even higher intelligences beyond this world.

Unfortunately the full-length episodes of The Twilight Zone have been removed from YouTube but here is a brief glimpse of this story...