Stop - and disregard what I said above.
Do not apply battery voltage to the GRAY/PURPLE terminals. Those leads go to ground.
The way the wipers work is:
The motor always has 12VDC supplied at the common brush and the switch on the column changes which winding gets grounded - and runs the motor. Sorry about the mis-communication.
Yeah - what you suggest above would be the case if you have a grounding problem in both the high & low speed leads. But I wouldn't bet the farm on that being the answer.
More likely you have a mechanical binding issue in the linkage or a motor that is just old and tired.
While the ground from the high/low windings comes out on two different brushes - the armatures share a common brush to provide power. So if the common brush is worn or the commutator is loaded with crap - neither set of windings will run the motor properly.
Permanent magnet motors usually have three brushes, common, low and high speed. Motor speeds are determined by completing the circuit to the low or high speed brush, while the common brush is used at both speeds.
That is how GM describes it. It might be more accurate to say "Motor speeds are determined by completing the circuit
FROM the low or high speed brush...
Here, see if these dwgs help at all - I am not very articulate this AM:
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