I managed to get some pictures when I got home today. Unfortunately the pictures arent great since it was a 4 hand job to hold everything for the picture. Anyway when looking at the plug with the middle pin toward the bottom, the pin on the left is Positive, and the middle bottom pin is negative, right side is not used.
When looking at the plug receptacle on the Push to test box you can go by the pictures below (I'm pointing the red positive probe at the positive contact, and the negative black probe at the negative contact.) hope this clears it all up for you.
For what its worth, I put an LED worklight on top of the solar panel to test it (since its dark here) and the voltage at the plug was 20v.