1986+ Mercury 6/8/9.9/10/15HP 2-stroke Factory Service Manual, Page 213Get this manual
POWER TRIM
Troubleshooting the Down and Up Circuits (All Circuits Inoperative)
Check in-line fuse (under cowl) to see if fuse is blown
Blown Fuse: Correct problem that caused fuse to blowReplace fuse
Fuse Not Blown: Connect Voltmeter RED lead to Point and BLACK lead to groundBattery voltage should be indicated
Battery Voltage Indicated: No Voltage Indicated: Check battery leads for poor connections or open circuitsCheck battery chargeBattery Voltage Indicated: Check black ground wires for poor connection or poor ground, Point 10Pump motor is faultyRefer to Motor and Electrical Tests Repair, followingBattery Voltage Indicated: Trim switch is faulty or there is an open circuit in wires (GREENWHITE, BLUE-WHITE) between trim buttons and trim pumpCheck trim switchCheck all trim harness connectors for loose or corroded connectionsCheck for pinched or severed wiresConnect Voltmeter RED lead to Point and BLACK lead to groundDepress Up trim button and check for battery voltage