I have a 1964 Plymouth fury station wagon. The car has an electric rear window. It can be controlled by a knob on the dash or turning of the key in rear door. Basically it doesn't work right. Main issues are. - Turning the key will make it go down, but not up. - Turning dash knob will make it go up, but not down. - The dash knob only works when I rev the car to a higher RPM than idle. The window also goes faster as the RPM's rise. Is this a wiring issue or is the motor shot?