Do you have voltage @ the #2 fuse?

Have you traced any wiring that goes to the 3rd light and tested for voltage there?

Could simply be a defective wire, broken inside the insulation. It happens more than you think, and ususally occurs near the termination points (like the contacts). I don't suppose you have any insulation piercing probes...?

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A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.