Hi,

Things could actually be worse!! You believe you saw smoke from somewhere and if so then that gives you an idea where to look. Also you have a clue in the broken tach. Also if there was smoke then there should be visible evidence of something "burning up" that you should be able to find through visual inspection. Obviously a schematic and the ability to read it (I am an electronics guy but still struggle with the Mercedes schematics) will help but it is not absolutely necessary. Some smart person might tell you where to look. In the mean time if you are so inclined, pull out the area where the smoke was and inspect for the burned area. Then fix what you find. Good luck!

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra