I have an old moped that has lots of the same type of connectors and they are always coming loose. In lieu of a wiring diagram, I have found that you can often tell where they're supposed to go by the way the wires are bent. In your pic, it looks to me that the wire on the left connects to the top prong, and the wire on the right connects to the middle prong. Totally unscientific, I know, but that's my gut feeling.

Is there a positive or negative sign marked on either the connectors or the prongs?