Possible reason for problem: Hooked up a multimeter to the cigarette ligther and drove car....found with AC, Lights and Aux Fan on, voltage could drop to as low as 11.3 V in idle and no higher than 13.2 with all accessories off at high speeds

Voltage regulator problem? It's on back of alternator right? (I actually bought a rebuilt MBZ alternator so you'd think it wouldn't be defective?

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1) 84 300SD 285K+ Miles (Ver Calif)
2) 84 300SD 175K+ Miles (Ver Federal)