Check your MAS relay by replacing it with a good used one. If you check the DTC (diagnostic trouble code) plug, you should see that the number of blinking lights will tell you that you have an issue with your MAS.

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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