If I am not mistaken you should have a direct feed from the switch to
the blower motor on high settings. There should be a resistor block in
between the two somewhere near the blower motor. if the motor turn on
lower speeds that means the blower motor is okay. I would check for
broken wires or connections at the connectors by looking for pushed
back terminals in the connectors. if you don't see any, check for
continuity at the motor to the switch. and work your way back to one
end or the other. Stopping at each connection in between.