Yeah, You should get a multimeter and test for continuity across each key position.
But if you don't have one and cannot wait. I believe B is your hot from the battery (after the main fuse of course), Turn the key one position and it hots up IG, turn the key to the number 2 position and it hots up both IG and L.
But like Grepper said, get a multimeter. This is a tool you should have before you ever touch the wiring on your bike. You can diagnose just about every electrical issue possible with a $20 meter.