The ground wire goes to one of the mounting bolts, not one of the terminals. A ground on either terminal will cause a short circuit and that is why you burnt the ignition to coil feed wire from the fuse box.

http://catalog.worldpac.com/mercedesshop/sophio/image.jsp?title=Ignition%20Coil&url=http%3A//img.eautopartscatalog.com/live/F300034900BOS.JPG

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A Dalton