Odd Blower Speed Problem

[TrailerTrash]

sorry if this is long winded im just trying to get to the bottom of this issue

i have a 79 k10 that originally had A/C. everything AC related had already been removed when i bought it. the only thing that is still there is whatever is inside the airbox under the hood and the wiring around it.

all the electrical connectors are still hooked up except for one round rubber 2 wire plug with green wires coming from it. the plug is about the size of a ping pong ball. nothing appears to have been changed or jerry rigged as far as the wiring it all looks factory.

the blower motor has a good ground and always works(stays on all the time on low).

the first problem is that the blower only works on low and high. it stays on the lowest speed for the first 3 notches then will be on high on the high notch. thats not a big deal for me BUT i have to have the switch kinda "halfway" between the 3rd and 4th(highest) notch for the blower to actually run on high. so i have to switch it to high then back it down slightly and get it to stick just below high for it to run on high.

i have tried 3 different switches(2 used and 1 brand new) and the problem is still there exactly the same with all 3 switches.

i can deal with only low and high but when its on high all it takes is a bump in the road and the switch gets jarred out of the sweet spot

i am in no way an electrician lol

thanks for any input in advance