The light system uses a switch, it's either open or closed. No resistance to check. If you're in question about the light working turn the key on and pull the connector from the switch and ground it with a jumper. the light should come on. Make sure you have a good connection to ground. If not, check the bulb. The light systems would come on at a pretty hot temp, about 245 or so. And to address this now, the light does not come on when you start the car and go off like the oil and gen lights. Only in an overheat condition.