Mercury Mariner 200, 225 Optimax Outboards Service Manual, 90-855348, Page 76Get this manual
Diagnosis of Alternator System on Engine 1If problem is an undercharged battery, verify condition has not been caused by excessive accessory current draw or by accessories which have accidentally left on2Check physical condition and state of charge of batteryBattery must be at least 75 (1.230 specific gravity) of fully charged to obtain valid results in the following testsIf not, charge battery before testing system
3Inspect entire alternator system wiring for defectsCheck all connections for tightness and cleanliness, particularly battery cable clamps and battery terminalsIMPORTANT: RED output lead from alternator must be tightA darkened RED sleeve indicates lead was loose and becoming hot4Check alternator drive belt for cracks and frayingReplace if necessaryCheck belt tensionAdjust if necessary, as outlined under "Drive Belt Replacement and Adjustment