the locking cylinder has a small button that fits into a matching hole in the door handle, keeping it in the proper location and preventing it's removal. When a key is inserted and turned just a bit, it allows the pin, or button, to fall into a grove inside the cylinder, removing it from the hole in the handle and allowing the cylinder to be removed from the handle.
I can currently lock the rear door, but need to crawl inside to unlock it. A pain!!
No you don't. Here's how the Courier back door key works:
To lock; insert key in the cylinder and turn 3/4 of the way around in the clockwise direction, then back again to the straight up position. Remove key. Push the door handle button and it will not allow you to depress it.