Once upon a time we had 150 or so E-series vans in our fleet. Replacing the blower motor, resistor, and resistor pigtail was a very common occurrence. To quickly diagnose a bad blower motor:
Turn it on to each different speed. Did it work any any speed but not all of them?
Yes - it’s almost always the resistor or blower switch. VERY rarely do we have wiring issues on that circuit.
No - Turn it on high and hit the blower with a handle of a hammer (or similar object). If it turns on, you’ve got a bad blower motor. Replace the blower, resistor, and resistor pigtail.(The resistor and pigtail tend to become 1 due to rust and age.)