1998 Mercury 9.9/15HP 4-stroke outboards factory service manual, Page 58Get this manual
IGNITION
Ignition Coil
The primary (+) side of the ignition coil receives voltage discharged from capacitor in the ignition (CDI) circuit located inside the ECMThe voltage is multiplied by the coil until it can jump the spark plug gapThe ignition coil will produce high voltage current each crankshaft revolution, producing spark at each cylinder at the same time (Waisted Spark Ignition)Ignition coil maximum output is approximately 40,000 volts
Ignition Test Procedures
Direct Voltage Adapter (DVA)
WARNING
DANGER HIGH VOLTAGESHOCK HAZARD! Do not touch ignition components andor metal test probes while engine is running andor being "cranked"STAY CLEAR OF SPARK PLUG LEADSTo assure personal safety, each individual spark plug lead should be grounded to engine