Seems to be the power supply to the blower motor. Try disconnecting the wire harness to the motor and/or resistor pack. I don't have a schematic, but typically the wire harness plugs into a resistor pack that is attached to the blower motor. On some cars however the resistor pack is placed somewhere else and attached via the harness. In either case, try re-seating the harness connector. If a wire is abraded it may be creating an "open" on the circuit and loss of power. Usually at the "high speed" setting the resistor pack is not part of the blower motor circuit, so if blower motor works on the high setting only, then the resistor pack failed. You'll just have to play around in there to determine what failed - wire/harness connector or resistor pack. (I doubt the blower motor failed as it works when it has power)
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