1998 Johnson Evinrude "EC" 9.9 thru 30 HP 2-Cylinder Outboards Service Manual, Page 138Get this manual
Temperature Switch Test Purpose
A heat sensitive switch is installed in the cylinder head to monitor engine temperatureThe switch is connected in series with the warning systemIf the 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 secondsIf boat is not equipped with System Check gauge, the warning horn will sound continuous tone
To ensure that the temperature sensing system can alert the operator during an overheating condition, test the warning system as described in Section 8, System Check Engine MonitorTesting
1Separate the connector and remove the temperature switch from the cylinder head
2Using continuity light or ohmmeter, make positive connections to the switchone lead to the switch lead and one lead to the metal portion of the switch