The linkage may have broken, or it may have popped off the motor, and
is now just resting on top of the pin that's supposed to actuate it.
Open hood, remove plastic cover on firewall, remove drivers' side half
of cowl vent panel, check linkage. The linkage is held onto the
motor's drive pin by a special kind of springy clip. If the center
part of that clip breaks, the clip will just fall off, and the linkage
will pop off very easily while the wipers are in use.
I couldn't find an exact replacement for that clip, so I just made
something out of sheet steel (cut a slot in it with tin-snips).
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