2004-2005 660 Yamaha Rhino Factory Service Manual, Page 391Get this manual
SIGNALING SYSTEM
5If the coolant temperature warning light does not come on when the main switch to "ON", or if the coolant temperature warning light does not come on when the temperature is high (more than 117123 (242.6253.4 F)): 1Bulb and bulb socket Check the bulb and bulb socket for continuityCONTINUITY 2Thermo switch Remove the thermo switch from the cylinder head Connect the pocket tester1) to the thermo switch Immerse the thermo switch in coolant Check the thermo switch for continuityWhile heating the coolant use thermometer to record the temperatures The thermo switch circuit is open and the coolant temperature warning light is off The thermo switch circuit is closed and the coolant temperature warning light is on