1986+ Mercury 6/8/9.9/10/15HP 2-stroke Factory Service Manual, Page 82Get this manual
CHARGING AND STARTING SYSTEM
No voltage reading; proceed to TEST 3aConnect voltmeter between common engine ground and Test Point 2bPush start switch
Battery Voltage
aConnect voltmeter between common engine ground and Test Point 3bPush Start Switch
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
Electric Start Tiller Handle Model
Neutral start switch on lower engine cowl is open or BLACK or WHITE switch leads are disconnected or damagedProceed to TEST 7
No voltage reading; proceed to TEST 5aConnect voltmeter between common engine ground and Test Point 4bPush Start Switch
12 Volt Reading
Neutral start switch is open, or YELLOWRED wire is open between Test Points and 3
No voltage reading; proceed to TEST 6Connect voltmeter between common engine ground and Test Point 5