[lkchris]

P21W is the German standard bulb for brake lights, backup lights, rear fog light, and turn signsls behind orange lenses. Has been this way since the 1970s if not earlier. By German standard, think every German car. If you have clear turn signal lenses, it's PY21W, which is physically not interchangeable ... that explaining why when you convert your early Boxster tails to later version, you need the newer bulb holder as well as the lens.