i have a 91 300e and have had ( as others have i'm sure )an alternator stop charging. The voltage regulator and brushes are a replaceable assembly mounted to the alternator - look up voltage regulator in the parts section to see what it looks like -when the brushes wear out the alternator stops charging and the dash light doesnt come on because the brushes are part of the circuit that controls the light. The warning you will get is when the voltage drops to something like10 volts the abs and airbag light come on and accessories get dim or slow. If you keerp driving the engine will die when there is not sufficient voltage. The part is easy to replace-you can even do it with the alternator still on the car