1973 duster temp sensor question

I have had trouble finding good heat temp sending units, even the brand new ones are bad at times.

I usually test the sending units with a test light clamp on battery + positive and poke the send unit terminal.

The test light should glow if working correctly. The more the engine warms up the brighter the bulb will be.

Don't know if the send uints are for a gauge or an idiot light?

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