I have a 2000 Ford -f-150 w/ triton v-8, 79k miles
My problem is that the fan only blows on high speed
I replaced the switch in the dash but it didn't help. Are there relays or something else I need to replace?
Could be the fan relays or resistors, usually located somewhere around the heater box. Or the switch itself has failed, in my experience, high speed only was a sign that the resitor pack had malfunctioned.