I wanted to add delay to my 85 Crew cab but need the switch. Why is the 85 part number different than the earlier numbers? I have been collecting the parts to change it over from 82-90 trucks. Why is the 85 switch different?

This is the slide switch down by the headlight switch. The 84 switch is the same as some of the 79 B bodys. Why wouldn't this part number work? Everything else looks to be the same on the 82-86 trucks? Will the 84 switch work in my 85?