Sometimes you can turn the wipers on high and move the wiper arm and then they may work. Also, when the wipers do work, they will stop in mid-wipe.
When I turn on my wipers, they just hum and do not work. on 1993 GMC 1500 Pickup
Remove the wiper arms and cowel cover. Check the pivot points at wiper assembly. They may be rusted not allowing wipers to move properly.
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I had that problem. There is a circuit board somewhere near or attached to the motor. It was flexing and causing problems according to temperature and humidity. I found the problem: a solder spot on the circuit board. I Fixed it and it came back. That board is a tight fit causing it to re-crack. Rather than buy one at a dealer, I soldered a piece of thermostat wire across the solder crack. Never had another problem in 10 years.