1996 Johnson Evinrude "ED" 40 thru 55 2-Cylinder Service Manual, P/N 507124, Page 303Get this manual
Trim Gauge Function 1Turn the engine key switch to ON position IE
ITJ 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