SC fluid over temperature sensor. It lights up the (idiot light) low-oil/warning light on the factory instrument pod if you over temperature the SC fluid. Out of curiosity/boredom I checked it out. It’s an Elmwood 2455RBV bi-metal thermostat. Searched on-line and found the specs on it. Specs are: Contact closes at 160F (+-2) contact opens at 130F (+-6). Bench tested it using a heat gun, multi-meter, and my hand-dandy Raytech MT4 infrared thermometer. The contact closed at 158F (warning light on) and re-opened at 124F (warning light off). The SC manufacturer states max oil inlet temp to be 176F so there is a bit of a safety margin even if you do get an over temperature light. Also note that if you do get a light the factory gauge pod has an automatic 1-min set/reset timer so if you get a light it won’t check again for 1-min unless power is removed (key turned off) which will reset the timer and you will get an immediate check. To isolate the warning light between engine low-oil and SC fluid over temperature just un-plug the engine oil tank connector. If you do not exceed the Rotrex max-rpm of 150,000 and get lots of airflow to that little SC radiator you will never get an overtemp light.