So things have been coming thanks to the help I've been getting here, much appreciated.

I think this is the last issue. I don't see any form of park brake. If I put the traction motor in neutral, it just seems to roll. I see a big brake wheel/clutch on the back of the traction motor, but I'm not sure if it should be clutching when put in neutral, and if so, what on the wiring diagram would actuate that (or actuate unclutching it when moving if that's how it should work). Everthing around that traction motor is pretty stuffed in there and not easy to see what's going on there.

For reference, wiring diagram is here: imgur.com/a/9ReVA (Copy and paste into browser address bar since I can't post a full URL link here)

I would assume this brake would also be the brake one gets when hitting the brake pedal, and that seems rather ineffective though if I haul on it hard, it will stop. I have filled the brake master cylinder with fresh fluid.