A data point on the voltage regulator for the alternator.

My 97 SL320 and C280 both have a resistor soldered across the regulator / one brush from the factory to keep the system operating even if the regulator fails in the no charge mode. The alternator won't put out full power but , if they sized the resistor properly, enough to run loads that never shut off + a little bit. ( Fuel pump, engine computer, maybe headlights too. ) Not all replacement regulators have this feature but it is easily added.