I don't think people are reading the entire conversation carefully. 05tbowner said his Euro headlights didn't come with a plug for the high beams, the housing had a positive and negative wire sticking out and he was asking if he had to splice in the stock wires to those but did not know which was positive and negative for the stock wires.
Then I said that for a regular halogen bulb, the polarity doesn't matter. However if you were to run an LED bulb the polarity would matter, because it wouldn't work in reverse. Somebody else mentioned that HID's had to be the correct polarity, and I said yes it would, but if you were to install HID's you would be changing out the entire bulb so the wires sticking out of the headlight housing wouldn't matter. With HID's the bulb connects directly to the ballast and not to the stock wiring.
So in conclusion, Halogen bulbs will work regardless of polarity. LED and HID bulbs will not work if the polarity is reversed. Hope that helps clear things up.