heater fan switch does not work on high

I have a 1998 s10 4.3 ext, The fan switch works on 1,2,3 but not on 4.
I've heard it could be a relay or resistor, has anyone had this same problem and fixed it?

I'm having the same problem. Its not the resistor pak (located in the engine compartment on top of the AC/heater box) which I changed because I had one on hand even if I knew better. Its not the speed switch either as I changed that first.
I'm thinking there is a relay somewhere, but have no manuals on this car (can't find any anywhere). If anyone has fixed this how about a posting?