Mercury Mariner V-250 V-275 Outboard Service Shop Manual 1990, Page 279Get 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 nOI trim up or down
1fPump motor operates
Engine trims up, will not trim down
Determine Power Trim pump motor operates when appro riate trim circuit Is
activated"