fan motor speed issue

[hogrocket]

Wondering if anyone else has ran across this issue. I'm trying to get my AC/heater to work. Initially, I was getting power to the motor, but the motor wasn't coming on. The motor worked fine when off and tested on a battery. I put it back on and cleaned/tightened all the grounds and it now works. That was probably just a grounding issue.
Now my current problem. When I turn the switch on low and medium speed works fine however, when I put it in high it goes back to low or off. Anybody have any ideas? I thought it might be the relay or resistor, but I thought I would ask you guys first. Thanks in advance. M