How long have you had the motor if they are dormant for any length time or bounced around on a mail truck the switch on the inside can get corroded or moved and not function.
When the switch plate is installed on the motor it needs to be clocked which requires the internals to be in a designated...
If you buy the 2 speed and use the 3sp switch it will not park and it will only have 1 speed.
I can restore your motor contact me if you would like
ns1aar.com
If its the original to the car it will be a reversing motor. Not parking correctly is usually a grounding problem. Check all your grounds including the switch to chassis This document will tell how to ID the 2 sp motors
Sometime in 70 Chrysler stopped using the red varnish on the terminals. If your motor fit within that time frame and didn't have it I would have not applied it, however if you would like to have it I can send you some.
Bruce