90 chevy van wiper motor question

[wvcab]

put  a new motor in ( the old one froze up), and the motor runs continiously, until you disconnect the wiper arms from the motor shaft. At this point the unit parks and all functions work (off, slow, fast), but * soon as the wiper arms are connected, the motor does not stop, and has slow(in the slow and off positions) and high speed. i measured the voltage on the motor shaft, and there is +12v between the motor shaft and the body.   defective unit (motor)? . I did disconnect the wiper switch, but it made no diiference. Ideas?

Robert

[enjenjo]

You have a shorted park switch in there. The motor runs until the park switch turns off the power.

[wvcab]

You have a shorted park switch in there. The motor runs until the park switch turns off the power.

ok... i went out and pulled the park switch off the unit, and seperated the contacts, the motor still runs, if the wiper arms are connected... what am i missing?

[enjenjo]

A GM wiper motor has power all the time. The switch inside the car operates it by switching the ground on and off. When you turn the swich on, it energises a solenoid on the park switch that closes the contact that completes the motor ground circuit. When you turn it off, the solenoid turns off, a cam follower is then allowed to open the contacts, stopping the motor in the park position.

If the motor runs continuiously, there are only a few thing that can be wrong. A short in the motor, a short in the park circuit, a broken park cam. If it was a broken park cam the arms being hooked up would not matter, so it is either the park switch, or the motor that is shorted to ground. It's difficult to diagnose long distance, but in most cases the park switch is the problem. If your motor has a delay, you might check the circuit board, as noted on another post, there can be problems there.  But regardless of the source, the problem is caused by a grounded circuit, where it shouldn't be grounded. I would look for a pinched wire somewhere myself, and since you just changed the motor, I would concentrate there, along with attached parts.