[Stickman77]

Can anybody tell me if the Temperature light is supposed to come on when the key is turned to the
ON position like the oil light does. It's a 1965 grand prix

[pfilean]

Not sure about 65 but 61 had green light and red light. Green came on with key in on position and would go off about 120 degrees. Red was tested for function with key in start position and would come on later at temp of (not sure) about 240 degrees.

[U47]

The Green and Red coolant temp lights and the oil pressure light come on when the key is switched on to verify they are working they remain on while cranking. The green light will stay on if the engine is cold until 114 degrees and will go out once that temp is reached. The red temp light comes on at 240 degrees. mot sure the green cold lamp is on cars from 65 on, but they are certainly on 59-64 cars
I use the combination Temp sender on other cars for engine oil temps / trans temps. NAPA still sell them.

[Stickman77]

I have a new engine harness and temp sending unit and the red temp light does not come on in the start position. I also replaced the bulb in the cluster. Any ideas

[pfilean]

I doubt the engine side wiring harness would effect the starting test of the light as the test function did not use the sensor unit on the engine as a ground during the test. Did you replace ONLY the engine side? Does the light work otherwise? Is the sensor on the 65 car a single terminal (only works when hot) or a two terminal (works when too hot or still cold). You can test the circuit by grounding the wire(s) at the sensor to see it the light(s) works then. But you may still have problems under the dash.

[LASJayhawk]

Should it come on, yes. There is a green wire going to the ignition switch that puts a ground on the light when you turn the key to start. You either have a bad bulb, bad wire, bad ground from the dash to the ignition switch(doubtful), or the switch is bad itself...