Mercury Mariner V-250 V-275 Outboard Service Shop Manual 1990, Page 290Get this manual
Fuse Test 1Use Voltmeter to check for battery voltage at terminall 1f no battery voltage is ind icated, there is an open circuit between terminal and positive (+) battery terminal Battery voltage must be indicated at terminal before performing next check
defecti veSet trim "Out" angle adjustment(Refer to "Trim Angle Adjustments"following If adjustment is O.K the trim limit switch is defective
Trim Sender Switch Test
1Trim engine to fullDown" position 2Discon nect trim sender switch leads (black wire and black wi re with brown sleeve) from junction block on power trim pump3Connect Ohmmeter (Rxl scale) leads between trim sender switch wires4Depress "trailer" button Ohmmeter needle should swing to the right as the engine trims upIf Ohmmeter does not swing to the right as the engine is trimmed up, the trim sender switch is defective
2Use Voltmeter to check for battery voltage at terminal2If voltage is indicatedthe fuse is O.KIf no voltage is indicated, fuse is blown Check for and correct electrical short that caused fuse to blow before replacing fuse