1987 Johnson/Evinrude CU Outboards 35A thru 55 Service Manual, Page 328Get this manual
Checking Sending Unit 1Connect an ohmmeter between sender unit terminal screw and oil line elbow With piston rod fully retracted, meter should indicate 90 ohmsExtend piston rod to end of travelMeter should read 0.5 ohms
Indicator Gauge Troubleshooting
1Connect voltmeter or test light between ground terminal and ignition terminal CD With ignition switch "On," meter should show 12 volts or higherTurn switch to "Off" 2Disconnect sending unit lead at gauge terminal Connect an ohmmeter Q) between sender unit lead and gauge ground terminal Low ohm scale should read 90 ohms with unit in down positionOperate unit to full trim up position, meter shou Id read 0.5 ohmsThe resistance change as the unit tilts should be approximately linear with no erratic movement of the ohmmeter needle3If checks and are ok, replace trim gaugeOHMS