These boards are designed to go in the roof of a 'G' gauge coach. They require 4.5v to 6v to operate. The current draw is approximately 30mA. There is a diode on the board to prevent incorrect polarity and a 100 ohm resistor to limit the current. You could change the resistor for other voltages. They are supplied as a pair. I do combine postage. Please check out my other listings.