[L16pilot]

I am not specifically familiar with the 69 Chevelle wiper motor, but I believe they all work similar in that the center terminal is 12 v hot all the time. The low speed terminal is grounded to start the low speed cycle. The high speed terminal is then grounded along with the low speed to achieve high speed wiper action. Then the high and low grounds must be removed in reverse order for the motor to park. My guess is the low speed wire is inadvertently grounded not allowing the motor to stop. remove the three prong plug and test either two outside terminals to see if you get zero-low ohms with the wiper switch in the off position. If you do...start tracing it back to the switch from there....could be wiring or could be internal to the wiper switch. Hope this helps