Mercury 35/40HP 2 Cylinder Outboards Service Manual PN 90-42794--1, Page 255Get 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
Outboard will not trim up or down
Determine 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 upf
Outboard will not return completely to "down" position or returns part way with jerky motion