Differences in coolant sensors

[EtaSport]

I have 87 eta. Does anyone know what the difference is between the yellow top coolant sensor, and the blue top sensor? I have a yellow top on my car that does not work at all. No continuity, no ohm readings. I know im testing it right because i did the same test on our other eta and i got readings.

So trying to find a new sensor and everyone is out of yellow top ones.
Autozone had the blue top listed for my car and I told the guy that was the wrong one, he didnt believe me.

[EtaSport]

Anyone? There are 4 of these things listed for my car. What are the differences? yellow top two prong, white and blue plug type, and a violet two prong..