ELECMAN

I have the factory gauges in the car the temp gauge sticks at 220.with the engine being cold it starts at a 100 and stops at 220.If i dont cycle the key on and off two times the guage wont go down.I spiked the gauge wire to ground and it goes from 100 to 300 so im assuming that the gauge is working.The sender has two prongs one is to the temp gauge,I think it reads resistance and the other goes to the idiot light.Im assuming its the sender is this correct