Riding with Death (1976)

Ever-so mellow Agent Sam Casey is in a satellite explosion and the radiation turns him invisible. He gets a watch that keeps him visible, and he uses it to switch from visible to invisible. He is assigned to transport a chemical called Tripolydine, which is purported to be the most efficient fuel; when the cover is blown on that and he uncovers and stops the Tripolydine fraud, he must then stop terrorist Robert Denby from blowing up racecars.