That looks like a dual voltage generator.It might be marked ; 6 volt goes to the small tail light and 12 volt goes to the head light. If you are thinking of two wires, one for positive +, and one for negative - , the bike frame acts as one of the wires. There is a grounding screw in the clamp that holds the generator on the frame. So the lights have to have good contact with the frame also. If you have a DC voltmeter you can check for the voltage from each terminal on the generator measured to the mounting bracket. Then read the voltage rating of each bulb.The wheel on the generator should ride on the side of the tire parallel to the tread.There is an adjustment on the bracket for that.