I tightened the belt, it was loose to the point that I could slip it over a pulley with mild to moderate force without loosening the tensioner. Lee, I took your advice and here are the readings at idle:
1. no load ~ 13.78v
2. lights ~ 13.4v
3.lights, a/c ~ 12.7v
4. lights, a/c, high speed aux fans, radio ~ 12.4v

all readings are an approximate estimation of where the multimeter was fluctuating. I'll see if tightening thee belt helped tomorrow

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1990 190E 3.0L