An old cartoon tv series from the late 60s or early 70s where a boy wore an amulet on necklace with P it and when he needed to help someone grabbed would say POWER?

The cartoon you're thinking of is "Shazam!"

Here's why:

* The Amulet: Shazam wears a magical amulet with a large "P" on it.

* The Phrase: When Shazam needs to transform into his superhero form, he yells "SHAZAM!"

* The Power: Shazam gains his powers from six ancient gods: Solomon, Hercules, Atlas, Zeus, Achilles, and Mercury.

The show aired from 1974 to 1977. It was a live-action show with a cartoon opening sequence.