I'd say it's as good a guess as anybody could give... Use a multimeter and check the resistance between A and B. The exact value isn't required here, just that there is resistance, and not closed or open. If you measure resistance, you got the coil leads. Check continuity between 1 2 and 3... guess you get the idea. No meter? Use a battery or some power source in the range the relay is rated at. Across 1 and 2, if its the coil, should hear a click (might need to turn the stereo down)