1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 236Get this manual
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Troubleshooting the "Up" Circuit (When "Trailer" Circuit Is OK) Remote Control Equipped with Trailer Button Use an Ohmmeter (R scale) and check continuity of wire between Point 10 on "Up" solenoid and