1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 324Get this manual
Troubleshooting the "Down" and "Up" Circuits (All Circuits Inoperative) Remote Control NOT Equipped with Trailer Button
Check in-line fuse (under cowl) to see if fuse is blown
Blown Fuse: Correct problem that caused fuse to blowS Replace fuse
Fuse Not Blown: Connect Voltmeter red lead to Point and black lead to ground, Battery voltage should be indicated
No Voltage Indicated: Check battery leads for poor connections or open circuitsS Check battery charge