2000 W202 Intermittent Low Voltage

[RobertR]

I am having an odd electrical problem with my 2000 C280 Sport.
When driving at night with the fog lights, high beams and rear defroster on (heavy load)
and either my radar detector or cell phone plugged into the lighter I will get what I can only describe as a brown out. The BAS / ESP lights on the instrument cluster will come on and the car will sputter.
If I unplug the detector or cell phone the car will return to normal.
If I turn off the highs the car will return to normal also. It seems to happen under heavy electrical load.
The Alternator and Battery were replaced about 13 mos ago by benz. Could this be a problem with either of these parts? Also I had an intermittent problem with the heater blower fan. It worked intermittently then stopped completly. When I investigated it looked like one of the fan motor supply wires was corroded. When I replaced the wire and corrected the connnection problems the fan worked. I did notice though that some times the fan speed would change on its own. Very irratic. Could this be a clue? The fan issue was recent (3 Mos)
Since this is intermittent and the car starts ok without hesitation I am stumped on where to look.

Any help or direction would be greatly appreciated.
Thanks in advance for your help.

Rob