1998 Mercury 9.9/15HP 4-stroke outboards factory service manual, Page 87Get this manual
CHARGINGSTARTING SYSTEM
No voltage reading; proceed to TEST 3aDisconnect BLACK ground wire from Test Point 2bConnect voltmeter between common engine ground and Black ground wirecTurn ignition key to "Start" or push-in the start button
Battery Voltage
aReconnect BLACK ground wirebConnect voltmeter between common engine ground and Test Point 3cTurn ignition key to "Start" or push-in the start button
12 Volt Reading
Check BLACK ground wire for poor connection or open circuitReconnect ground wire to starter solenoid; proceed to TEST 7
No voltage reading; proceed to TEST 4
12 Volt Reading
Defective starter solenoid
aConnect voltmeter between common engine ground and Test Point 4bTurn ignition key to "Start" or push-in the start button
12 Volt Reading
Neutral start switch is open, or wire is open between Test Points and 3
No voltage reading; proceed to TEST 5
No voltage reading; proceed to TEST 6Connect voltmeter between common engine ground and Test Point 5