Hi friends. I want to share the success story I experienced 2 weeks ago with my 350SD. I've been living with flickering lights for more than to years. The alternator was replace by the MB dealer. In my mind I was looking for an answer. I was even thinking on the ignition switch, because the radio was turning off intermitently at idle. Reading all the prime information that has been posted, the problem was limited to the Alternator, Voltage regulator or the connections in that area. I followed previous advice and measure voltage at the battery at idle (12.75V) at 1500 RPM it was 13V. I replaced the voltage regulator with a Transpo with a variable potentiometer. While doing my tests, I noticed the connection between the alternator and the battery (mine is one cable not two) was very hot. When I tried to tight the connection the bolt broke. I fixed the pole by drilling and tapping some 6mm x 1 thread, clean everything, retighten, and Bingo no more fickering lights, no more intermittent on-off of my radio, even with the high beam, A/C and rear defrost on. At idle volatge is still 13.5 but at 1500 RPM it goes to 13.9.
I am very happy of solving such a problem through the information in this forum. I am willing to help others the same way I've been helped.
Thank to all the members.