1998 Mercury 9.9/15HP 4-stroke outboards factory service manual, Page 93Get this manual
CHARGINGSTARTING SYSTEM
CHECKING POSITIVE BRUSHES AND TERMINALS 1Connect ohmmeter (R scale) leads between positive brushes2Ohmmeter must indicate full continuity (zero resistance)If resistance is indicated, check lead to positive terminal solder connectionIf connection cannot be repaired, brushes must be replacedRefer to "BRUSH REPLACEMENT"
aPositive Brushes TESTING NEGATIVE BRUSHES FOR GROUND Set ohmmeter to (R scale)Place one lead of ohmmeter on the negative brush and the other lead on the end cap (bare metal)If the meter indicates NO continuity, replace the negative brushRepeat this procedure on the other negative brush