1988 Johnson/Evinrude "CC" 40 thru 55 Models Service Manual, Page 325Get this manual
Checking Sending Unit Connect 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 ohms1
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 should 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 gauge3