Most of the time if you take it apart and check connections and brushes and wipe commutator with emery cloth and a general exam, you can get it operational. Plus you learn how it works. Not sure what your problem is but you can test it on the bench using your battery charger as a power supply because.............that's what it is. Give it a try. Sometimes they just need lightly oiled at shaft ends. Sometimes it's just the cable, switch, wiring or ground.
When I refreshed my 60 GMC motor it confused me for a while. One terminal was hot and the other was ground. I was used to the case being ground. So...............if you dig into it just be sure of the wiring when testing, If it's two speed, that will add to the equation. I don't think I've found a "dead" motor, wiper, fan, starter that I could not bring to life with just tinkering, cleaning, oiling, emery the shafts/commutators, free up slide switches, fix electrical switch or new brushes/brush springs.
Step 1: Take it to bench and apply power/ground directly to motor terminals. Sometimes with small motors, the commutator shaft can be chucked into a drill in a vise or in a drill press and apply emery cloth like a lathe. Clean between segments with a pick tool. Motors last a looooooong time.
This is all just my experience, not telling you what to do or not to do. It's just what I would do. There is absolutely no mystery to these motors.
