A 300SD uses the equivalent of 1156 bulbs for rear blinkers, stop lights and back up lights. It also uses 89 bulbs as rear running lights. W123's use this exact same combination. There's some disagreement if you should use American bulbs because the watt ratings are a little off (1156 is rated at 27W and the ECE bulb is rated at 21W), but there candle power ratings are identical so you can't tell the difference with them in use. You won't melt anything unless you install bulbs that are rated way too high like replacing stock 55/60W H4 headlight bulbs with 90/100 H4's. You can also buy 1156, 89, etc bulbs with nickel bases so they don't look any different then the Euro bulbs. Just go to the Sylvania website at http://www.sylvania.com/auto/carapp/ look up your 300SD and when in Walmart look up the other American equivalent bulbs for the Osram part numbers the Sylvania website lists. Hoped that helped.