1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 38Get this manual
16 Ampere Alternator System Test (SMALL VOLTAGE REGULATORRECTIFIER) 1Check battery voltage at battery with engine running2If battery voltage is above 14.5 volts, replace voltage regulatorrectifierCheck condition of battery as overcharging may damage battery3If battery voltage is below 14.5 volts, charge battery; refer to "Charging Discharged Battery", precedingIf battery can NOT be satisfactorily charged, replace battery4If battery accepts satisfactory charge, check battery voltage while cranking engine; refer to "Charging Discharged Battery", precedingIf cranking voltage is not acceptable, replace battery5If cranking voltage is acceptable, disconnect larger diameter Red wire from STARTER SOLENOID terminal6Remove smaller diameter RED wire (SENSE LEAD) from STARTER SOLENOID terminal and connect to the POSITIVE (+) terminal of VOLT transistor batteryGround the NEGATIVE () terminal of the VOLT battery to the engine7Connect RED (+) ammeter lead to larger diameter RED wire, and BLACK () ammeter lead to POSITIVE terminal on STARTER SOLENOID8Secure wires away from flywheel9With engine running at the indicated RPM's, the ammeter should indicate the following approximate amperes: RPM IDLE 1000 2000 3000 AMPERES 10 17 18