How many volts does an alternator put out. My 300SEL, 1988 alternator outputs between 1 - 2 volts, the car starts very well with 13plus volts, but when voltage is 12 and below the car won't start. You crank and wipers come on. How does the iginition coil factor in this case? If this coil is bad will the car fail to start or start randomly.