1998 Johnson Evinrude EC 50 thru 70 HP 3-Cylinder Service Manual, Page 273Get this manual
Trim Gauge Function
1Turn the engine key switch to ON position
The 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 1 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