When 'turned-on' to any position, the wipers 'jerk' up & down erratically in the area where they are normally located in the 'off' mode ('at-rest' position). I bought this truck new, and have never had this problem occur until now. Do you think the problem is the switch (off the steering column lever), the motor, or the linkage? Also...where is the motor located (can't see it under the hood), and have there been any tech bulletins on this problem? Is there any 'free' site that provides any service info (pictures/removal instructions, etc) for the wiper motor and associated components? THANK YOU.