Mercury Mariner 25HP 4-Stroke Outboard Service Manual 1997, Page 56Get this manual
Ignition Test Procedures Direct Voltage Adapter (OVA)
DANGERHIGH VOLTAGESHOCK HAZARD! Do not touch ignition components anellor 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
CAUTION
To protect against meter andor component damage, observe the following precautions: 400 VDC test position (or higher) MUST BE used for all testsINSURE the Positive (+) leadlterminal of OVA is connected to the Positive (+) receptacle of meter
00 NOT CHANGE meter selector switch position while engine is running andor being
ALL COMPONENTS MUST BE GROUNDED during testsRunning or "cranking" engine with COlor Ignition Coils ungrounded may damage components