I have a 1985 190E, and while I was at a stop light, I switched on the rear defroster, and I lost power to everything. I mean everything. No hazard lights, running lights, headlights,dash and interior lights, window motors, no power to starter, basically, everything is dead. What could be the cause and how do I diagnose it?

GOT IT FIXED!!!!!! As it turned out, it was not the alternator. There is a small terminal block in front of the battery, and the first thing I noticed was that it was melted. The wires that connect to it were totally corroded, I mean REALLY corroded. So, I pulled off the terminal block, pulled one off my parts car, then cleaned all the contacts thoroughly, replaced the screws with new un-corroded ones and it came back to life!!: I took some pictures of the procedure if anyone has any questions.