The circuit is simple. There are three pins on the connector to the resistor, and two more wires that go to the blower.

The RED wire on the three pin is battery voltage. The Brown wire is ground. The middle wire is the "control voltage" from the climate module. WIth the car off, is should have zero volts on it, if there is voltage, the speed of the fan is:

1.5 volts - low
7 volts - high

A bad climate module can cause this. Or, a bad (even if it is new) resistor can cause this too.