Driving, look down to see temp gauge maxed out. Stopped and checked things over. Engine warm, but not excessively hot. Let it sit for overnight, checked it out the next day. Turn the key to the on position, gauge maxed out. Checked the sensor, it works fine. From what I can tell, the higher the temperature reading, the lower the resistance on the sensor, therefor the higher reading on the gauge. Unhooked the wire from the sensor, checked resistance to ground, about 200 Ohms. Turn the key on, 0 Ohms. Something is shorting the wire to ground, only when the key is switched on. Any ideas?