I believe the black goes to the fan motor....check for power when the switch is on on the black terminal, if there is nothing, yet power on the other side of the switch, then it may be your switch...try some contact cleaner. If there IS power on the black wire side, then either your black wire is open or cut, or not properly attached to the back of the blower motor. The motor is grounded to the firewall thru the casing.

Did you check the resistor as well as the switch? Also, make up a long jumper cable, and connect it to the power and to the blower to test it.