Originally posted by EliteAccord
If I think what he is saying. It means one wire is for power and one is for ground. Granted it might plug in if the power wire is connected to the ground wire it won't work and the electrical flow won't flow all the way through. 
yea, basicly what he said. My the adapter for my aftermarket converter for 9006, to H4, the black and red wires were switched around.
check all your wires from the very start. Follow the red, and make sure, after every connection, it stays red, and doesnt switch to black