Mac seems to waver between his thinking and feeling functions. On the one hand, in times of crisis, he is the epitome of an ENTP. On the other hand, and despite strong initial opposition at first, he always follows through relationally if a friend is in need.
Pete Thornton: ESTJ
Pete is an administrator through-and-through. He makes sure that all the t's are crossed and i's are dotted, but his strong sense of right and wrong also yield an empathetic heart.
Jack Dalton: ESTP
Jack is the classic doesn't-look-before-he-leaps type and quite capable of convincing others to go along with his schemes. He has no regard for anything that doesn't produce sensation of some kind. Fast-talking and risk-taking.
Murdoc has a taste for the theatrical. He monologues, has wonderfully evil Rube Goldberg devices, and his ransom notes are always a delight.
Dr. Zito: INTJ
MacGyver's own Hannibal Lector rip-off, Dr. Zito has plans, contingencies, and more plans. Nothing he does is without specific reason.
Penny Parker: ESFP
Penny does not care for grand schemes or big ideas. She loves people. She loves the stage. Not much else goes on in her head.