Strange problem. My wipers will work normally for a minute or so then stop dead on the windshield. They will not return to the park position no matter how many times I move the switch back and forth. After letting the motor cool for several hours I can crank it up and the wipers will return to park and start working again. Only way I can use the wipers while out cruising and it starts raining is to turn them on for a few swipes and then back off for a few seconds. I do keep rainex on the windshield to help if I get caught in one of our frequent Florida showers. I’m thinking a heat related problem but where?
New motor. Do not purchase a rebuilt unit because most rebuilders do not replace the park mechanism in the motor.
Bad spot on the commutator, or possible ground/power connection. I would remove and clean wire connections and make sure grounding/bonding is good, then pull the motor and inspect it. I have cut the mica and resurfaced the copper and brushes on wiper (and other) motors and had them work for many years. (I am not a fan of the cheap parts available, and will try to salvage on OEM part first.)
