This sounds to me like a ground issue.

I had a similar issue on my BMW. I fixed the loose ground and the problem went away.

On my 300SD the gound is a brown wire attached to a post under the instrument cluster. Try pulling the clustger and checking for any loose brown wires. I would also check the ground strap for the body, engine and the negative post on the battery.

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Monika '74 450 SL
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'97 Jeep ZJ Laredo
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'92 Subaru
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