My 77 K25 non-ac has a 4 position blower switch, HI, MED, LO or OFF can be selected. Face plate labeled OFF at bottom & HIGH at the top with a 4-blade fan graphic to the right of the switch slot in the face plate. Have had this truck for 43 years, pretty sure it's the original configuration. Yes I've seen trucks with the 3-position, don't know the reason for the difference.