I know this is a Mercedes Forum, but something you said seems wrong: " 3rd - removed ammeter - using a 1.5 Volt D size battery & flashlight bulb, I connect the new ammeter in series. The meter read > 10 amps. Ammeter appear to be working!"

How can you get 10amps out of a "D" cell?

I'm no pro but that just doesn't seem doable.

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1993 190E 2.6 135k
1989 Ford Thunderbird SC 5 Spd 79K