1998 Johnson Evinrude "EC" 90, 100C, 105C, 115, 150, 150C, 175 60 deg. LV Service Manual, P/N 520210, Page 154Get this manual
Temperature Switch Test Purpose One heat sensitive switch is installed in each cylinder head to monitor engine temperatureBoth switches are connected in series with the warning systemIf either switch senses temperature in excess of predetermined limit, contacts close and cause the System Check gauge "WATER TEMP" light to turn on and the warning horn to sound for ten seconds
To ensure that the temperature sensing system can alert the operator during an overheating condition, test the warning system as described in Section 7, System Check Engine MonitorTesting
1Separate the connector and remove the temperature switch from the cylinder head2Using continuity light or ohmmeter, make positive connections to the switchone lead to the switch lead and one lead to the metal portion of the switch3Place the switch and an accurate industrial thermometer in warm automotive crankcase oil