That light is not the oil temp light, it is the coolant temp light. If it comes on while riding, it usually means the quad is overheating. The fan should also be on. If the quad is overheating, then you should shut it off when the light comes on. Check coolant level and see that the radiator is full.
Now from what you say, the quad may not be overheating. If the quad sits for a couple of hours and then you start it, does the light stay on? If so, the temp sensor could be bad and may need to be replaced. If the sensor is good, it could be a wiring problem, need to check over the harness.
2004 TRX450R, 2008 TRX700XX
(BITD #639 Quad Ironman Expert)
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