1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 312Get this manual
Troubleshooting Determining if Problem is Electrical or Hydraulic
When problem is encountered with the Power Trim system, the first step is to determine whether the malfunction is in the "electrical system" or the "hydraulic system Refer to the following chart to determine which system is at fault
Problem Chart
Outboard will not trim up or downDetermine if Power Trim pump motor operates when appropriate trim circuit is activated
Outboard trims up, will not trim down
Outboard trims down, will not trim upPump motor operatesPump motor does not operate