Sounds like an alternator problem to me, too, possibly caused by a short elsewhere. I had a similar experience several years ago. Driving in a light snow, about 35 mph, my headlights dimmed and most dash panel lights all lit up and the car just died in a manner of seconds -- no warning or hint. I was lucky to coast into a shopping center parking lot then have the car towed to a great local MB mechanic. But even they can be fooled.

He installed a new alternator and it burned out, too. He eventually tracked the problem to my radio antenna cable. There had been a mild rust bubble in the paint where the antenna seats into the rear fender. Apparently the wet snow helped caused the antenna to ground and short out the alternator. For a quick fix, he simply cut the antenna cable. I later had the rust dealt with, repainted the fender, and installed a new antenna.