http://www.overgrow.com/growfaq/1577 (http://www.overgrow.com/growfaq/1577)
http://www.onlinepot.org/grow/wiringlights.htm (http://www.onlinepot.org/grow/wiringlights.htm)
Has a nice explanaition for you if you are wanting to use 120v. I can also tell you that some of those ballasts can be wired for different voltages and have different wires for different voltages so you may have wires there that you don't use. Also being as this ballast was obtained from the street it may not have the correct wires for the desired voltage.