1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 239Get this manual
Troubleshooting the "Up" Circuit (When "Down" Circuit Is OK) Remote Control NOT Equipped with Trailer Button
Connect Voltmeter RED lead to Point 10 and BLACK lead to groundDepress the "Up" trim button
Battery Voltage Indicated: Connect Voltmeter RED lead to Point 3
No Voltage Indicated: Trim Switch is faulty or there is an open circuit in wires [GREEN-WHITE, BLUE-WHITE and PURPLE-WHITE (or PURPLE)] between trim point and trim pumpD Check trim switchD Check all trim harness connectors for loose or corroded connectionsD Check for pinched or severed wires