1987-1993 Mercury Mariner Outboards 70/75/80/90/100/115HP 3 and 4-cylinder Factory Service Manual, Page 229Get 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
Trouble Chart
Engine will not trim up or downDetermine if Power Trim pump motor operates when appropriate trim circuit is activated
Engine trims up, will not trim down
Engine trims down, will not trim upPump motor operatesEngine will not return completely to "down" position or returns part way with jerky motionEngine thumps when shiftedPump motor does not operate