1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 54Get this manual
CHECKING POSITIVE BRUSHES AND TERMINAL Set ohmmeter to (R scale)Connect meter leads between POSITIVE brushesMeter must indicate full continuity or zero resistanceIf resistance is indicated, inspect lead to brush and lead to POSITIVE terminal solder connectionIf connection cannot be repaired, brushes must be replaced STARTER SOLENOID TEST 1Disconnect all wires from solenoid2Use an ohmmeter (R scale) and connect meter leads between solenoid terminals and 23Connect 12-volt power supply between solenoid terminals and 4Solenoid should click and meter should read ohms (full continuity)4If meter does not read ohms (full continuity), replace solenoid