1986+ Mercury 6/8/9.9/10/15HP 2-stroke Factory Service Manual, Page 71Get this manual
CHARGING AND STARTING SYSTEM
Alternator Amperes Output 1998 And Prior (StatorPole4 Pulse)
Amperage output can be measured by installing amp meter (10 amp minimum) in series between the rectifier and the battery or by clamping an inductive type amp meter (10 amp minimum) over the RED output lead from the rectifier to the battery
NOTE: Acceptable alternator amperage output should be within 10 of the amperes listed belowRPM Idle 1000 2000 3000 4000 5000 6000 AMPERES .9 2.5 3.5 4.0 4.3
Alternator Test (1998 And Prior)
NOTE: Alternator can be tested without removing from engine1Disconnect GRAY and YELLOW alternator leads from terminals on either rectifier, voltage regulator or isolator block2Use an ohmmeter and perform tests as shown in following chart3If meter readings are other than specified, replace alternator assemblyTest Leads