Tail light I bought was a dual filament bulb setup. I added the third wire by mounting it to one of the screws that holds the actual light assembly into the tail light housing. ( I beleive this to be a simple ground), May have been just dumb luck but when I found the right combination to the existing wiring harness it worked perfect. Compared the current draw to that of the stock tail light with no difference. Like I said probably just dumb luck but need that every once in a while