The Greatest American Hero (1981)

Ralph Hinkley was minding his own business, a teacher on a field trip with his high school students, when the bus he's driving mysteriously drives itself out into the desert. A startled Ralph is soon visited by aliens, who had decided to endow him with superhuman powers to fight the battle against injustice and crime. To this end, they gave him a special suit and an instruction manual. Unfortunately, Ralph managed to lose the instruction manual, and the aliens have a nasty habit of never being around when you need them.