Below are two Magnum P.I. intro theme songs. The first one is probably the one most associated as its theme song—the one with the catchy guitar riff. The second one (I think) was the one used for the first few episodes of the first season. As for now I have no further information about the theme songs. Damn it, two posts in a row.
About Magnum, P.I.
Magnum P.I. is about the adventures of Thomas Sullivan Magnum (played by Tom Selleck), a retired U.S. Navy official who became a private investigator (hence, P.I.) in Oahu, Hawaii. The show ran from 1980 to 1988 on CBS and was created by Donald P. Bellisario and Glen A. Larson.
The car in Magnum, P.I. is a Ferrari 308GTS.
Watch & Listen – Version 1
Watch & Listen – Version 2