1998 Johnson Evinrude "EC" 25, 35 HP 3-Cylinder Outboards Service Manual, Page 243Get this manual
System Check Engine Monitor
The OMC System Check engine monitor warns the operator of conditions that could damage the engine; The monitoring system consists of dash-mounted gauge with four light emitting diodes (LEOs), warning horn, sensors on the engine and oil tank, and related wiringThe system is compatible with the OMC Modular Wiring System