Heater motor only runs on high speed

Do I have to pull out the complete switch assembly, or could it be some thing else?

Most likely the problem is with the blower motor resistor pack. This is located under the passenger side dash mounted to the heater box next to the blower.

Tester

It’s almost certainly the blower speed resistor pack. Of course, your blower may be drawing excessive current. In that case, both the blower motor and the resistor pack would need to be replaced.

Thank you very much

Thank you also very much