Idiot Light Question

[Short 3/4]

I'm curious about the "bulb check" feature on the standard non gauge dash. When I first turn on the ignition both the 'oil' and 'gen' lights go on until the engine starts (as they should). Are either of the red or green 'temp' lights supposed to do the same?
A related question, how cold does it generally have to get for the green light to light when the truck is first started? I've only seen that light flicker briefly once in over 30 years. Of course it doesn't get as cold here as a lot of you see, but even on winter trips to the hills I've never seen it light (and yes, the bulb is good)
Thanks for any help
Tom

[AcampoDave]

My buddy's '66 will have the cold light on until the motor is fairly well warmed up. Even on a San Joaquin Valley summer night. All the vehicles I've had will light the temp lifght in the cranking position for driver verification of their function. A dedcated lead on the ignition switch provides the temporary ground when the key is in "start"

[Johnie]

Yes, the green light on my 64 comes on until she warms up. That's about the time I can turn off the choke. Check the wires at the sending unit maybe?

[Short 3/4]

Thanks for the help guys. Looks like I have some wires to trace, and maybe a new sending unit in my future.

[Wrenchbender Ret]

Around here your teeth chatter till the green light goes off & you can turn on the heater.
It should come on every time you start the engine cold & stay on till heat starts to circulate.
George

[jayoldschool]

I did a new sender in my 230 when getting it road worthy. Green light never comes on. Red does. Works on my Impala, though.

[Superduke]

I have new sending unit in my 250 the green light is on all the time. I'm thinking another new unit but could it possibly be anything else.

[AcampoDave]

Sender wire could be grounding out

[Johnie]

The circuit for the temperature works like this:
Positive current is supplied to the bulbs when the key is turned on.
Ground is provided by the sending unit if it is hot or cold.

To test the bulbs you can pull the two wires off the sender and ground them out. This should make the green and red lights come on when you turn on the key.

Testing the sender for overheating (red light) requires getting the sender hot. Maybe use a heat gun? Or take the sender out and heat it with a lighter? Testing the sender for cold (green) is easy - green light goes off when the heat blows warm.

Superduke: If you pull the wire off the sender and the green light still stays on you have a short to ground in the wire to the bulb. If the green light goes out when you pull off the wire but you get warm air out of your heater then Id blame the sender.

[Wrenchbender Ret]

If the green light stays on all the time its possible the thermostat is bad & the engine is not warming up.

[jayoldschool]

It will still get warm enough when the engine is running and the truck isn't moving with an open stat.