70 malibu, non a/c car. Is there any reason the 2 middle speeds would work and not the high speed? Could the resistor cause this? I was under the assumption that the resistors are bypassed when on high. I have tried 2 different switches, what are the odds that both switches are defective?

My odds are usually no good. Yes, the resistor is not used. On your switch connector, brown is the input 12 volts. In high speed it connects to the output wire which is orange.

The high speed portion of the circuit is sometimes fused separately. Check for a fuse on the firewall, upper area, near a relay. This is where I found it on a 70 chevelle.