Yes, one of the pins is supposed to be earth .

Yes, circuit boards often get "opens" in the circuitry making repairs necessary .

This is where taking some time to trace the ground paths with a TEST LIGHT (never a meter because it often gives false positives) and battery to discern exactly where they go, they meander all over the place .

FWIW, if you ever find the number 31 that's a direct to ground circuit and DIN codes say it should be BROWN .

I have no idea what the junkyard situation in Beruit is but I have old Chevrolet and GMC buddies who are constantly sending me junkyard images of old trucks so I imagine there are Mercedes out there somewhere .

Even the most mangled ones will usually surrender good harness bits, bulb sockets, proper hardware, on and on.....

It's nice to be rich and just cut checks at the Mercedes dealership but most of us still here now are average working Joe's who have to account for every penny yet still want to drive a nice old 'Benz .

Most German gauges are designed to work on 12 volts directly but in general it's bad practice to apply straight 12 VDC to a gauge head or sender .

Do the rest and every time you find a contact, polish it using metal polish or cleaner typ wax, never use sandpaper, wire brushes, sharp edges and so on ~ electrical contacts are delicate and only pass minescule amounts of current so they're easy to damage .

Take your time here .

What you learn now will be very useful when (if) you go back to Old Blighty and decide to up fix a Morris Minor like your Mum had....

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better