Many higher quality contacts are electroplated....silver or gold...a lot of those on the Benz are sliver plated at least some of the older ones....abrasives will quickly remove that plating permanently, simple brass is most common however. I prefer to use a good electrical contact cleaner on both the male and female connections and plug and unplug them several times quickly before it dries...then use a dielectric grease liberally applied to both plug and socket to prevent new oxidation.

There are proper tools for burnt contacts....its not an emery board or sandpaper...its called a burnishing file....and they are very fine and seem almost smooth. Not many people outside of my line of work even know what those are.

You can find them at electronics supply houses.

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Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
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Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche