Mercury 35/40HP 2 Cylinder Outboards Service Manual PN 90-42794--1, Page 194Get this manual
Troubleshooting the "Down," "Up" and "Trailer" Circuits (All Circuits Inoperative) Fuse NOT BlownConnect Voltmeter red lead to Point and black lead to Point 3Battery voltage should be indicated
Check to see if in-line (located under engine cowl) is blownFuse Blown: Correct problem that caused fuse to blow Replace fuse
Battery Voltage IndicatedConnect Voltmeter red lead to Point 10Depress trailer button and check for battery voltage
No Voltage IndicatedCheck battery leads for poor connections or open circuits Check battery charge Test "square" fuse on trim pumpRefer to "Testing SolenoidFuse, and Trim Pump Motor Test thermal overload switchRefer to "Hydraulic Trim Pump Motor Testing ," see Table of Contents
Battery Voltage Indicated: Pump motor is faultyRefer to "Hydraulic Trim Pump Motor," see Table of Contents
No Voltage Indicated: Connect red Voltmeter lead to Point 11, and black lead to ground