i have a 85 300D and have been down this same road, mine had a land burnt off the circuit board, i used some small guage wire and repaired it, using a small 25 watt pencil soldering iron. everything is working fine now. however,,,, i had already ordered a new relay from mercedes, they wouldnt return it because it was a special ordered part. if you need a new one, i will sell it at a discounted price.

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matt