1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 238Get this manual
Troubleshooting the "Down" Circuit (When "Up" Circuit Is OK) Remote Controls With or Without Trailer Buttons Connect Voltmeter RED lead to Point and BLACK lead to groundDepress the "Down" trim button
Battery Voltage Indicated: Connect Voltmeter RED lead to Point 9
No Voltage Indicated: Connect Voltmeter RED lead to Point and BLACK lead to groundDepress "Down" trim buttonIf battery voltage is indicated, wire is open between Points and 1
Battery Voltage Indicated: Connect Voltmeter RED lead to Point 2D Depress "Down" trim button
No Voltage Indicated: There is an open circuit between Point and positive (+) battery terminalD Check for loose or corroded connectionsD Check wires for open