Green’s Dictionary of Slang

(orig. US) energy, enthusiasm.

1966		H.S. Thompson letter 28 June in Proud Highway (1997) 577: A lot of the original zap is gone from the book.
1974		‘P.B. Yuill’ Hazell Plays Solomon (1976) 29: I felt like Superman — but I could not deliver the final zap and wowie.