Had a similar problem on the left side of a 124, our lights were not going out, but the left side would dim. The problem was the ground connection in the metal strip which the bulbs push into. Follow the brown wire in that metal strip, and you will see that it is simply pinched in a groove. We removed that metal strip by cutting off two black plastic tabs that retained it and then squeezed the metal bar tighter, pinching the wire tighter and reinstalled the metal strip, solving the problem. You should reglue the tabs when reinstalling the strip. Hope this works for you.

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