If you can't start in Park or Neutral, then it's likely to be the Neutral Safety Switch. Could the starter be stuck? Just in case, the ignition key needs to be turned of then on again, after shifting into neutral gear, to re-engage the starter.

Good luck.

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03 CLK430 Cabrio 211K Pweter Silver/ Oyster Leather
90 300SEL 214k Pearl Black/ Alto Grey/Black Leather

Prior: 85 190E, 88 300TE, 89 300TE, 90 300E 2.6, 90 300TE, 92 300E 2.6, 91 and 93 300SL, 87 Ferrari Mondial Cabrio