should be a three pronger attachment. in the instructions it should tell you which one is the high and which is the low.. if not usually black is ground... or find the ground wire... and from there switch the other two
same thing happened to me while installing my friend's HID kit. Those kits are made to plug into the passenger side headlight harness, but because the battery is on the driver's side on our cars we have to plug it into the driver's side headlight harness since the wiring wont reach. Because of that, the wiring is backwards, you juist have to switch the wires around.