tracing out the circuit:
there should be a connector(connectors) under the hood near the blower) wih Purple/green, Green/Yellow, and Green/Slate wires.
Disconnected, Purple/Green from the dash/bulkhead (not going to the blower) should have 12VDC (to a good ground) with ignition on.
Green/Slate should be zero resistance to ground with dash switch in high speed (second click)
Green/Yellow should be zero resistance to ground with dash switch in Low speed (first click) - if not, the switch has an issue - if ground is good in this setting, switch is good and the low speed resistor is probably shot.
The resistor is mounted in the blower housing (riveted in on a plate IIRC). Resistance should be read between Purple/green and Green/Yellow through the disconnected blower connector. If not, that resistor is probably shot.