1997 Johnson/Evinrude EU 25, 35 HP 3-Cylinder outboards Service Manual, Page 259Get this manual
Trim Gauge Function
1Turn the engine key switch to ON position
2The boat trim gauge should indicate full trim-up when tester TRIM SNDR switch is in UP position, and indicate full trim-down when tester switch is in DOWN position If gauge needle does not move, check instrument harness whitetan, black, and purple circuits for an open If gauge needle moved in one direction but not the other, replace trim gauge