Hi does anyone know what the third ring terminal is for? One is positive one is negative and the third says “thread in probe” ???

 

What about it?
You just posted a picture, which, by the way is NOT a stock GM harness. It uses 3 separate relays instead of the stock GM relay/fuse block
Also, there aren't plugs for two fans.
This is aftermarket, which usually comes with instructions.

 

Ahh ok I was under the impression that it was a stock replacement harness.also the instructions said one connect ground, positive and thread in probe. And the 2 pins to the ecm. I’m assuming it will work for my swap but I just don’t know what it means by “thread in probe.

 

Maybe means to thread into the temp sensor, which is not needed if that is controlled by the PCM.
Three Relays are there and I take it fuses in that red box.

You're clearly overlooking them two large plugs there with the black and red wires going in them.

 

Ah.... I just looked closer and realize one is flipped sideways, making it look like a smaller plug. You're right, of course!

 

No worries. They look like the plugs on the 2004-up stuff.

 

@the_merv that is what I was thinking as well. I will have to follow all the wires and draw up a diagram of how they all run and connect. I’ve read some horror stories about these harnesses being sold wired incorrectly. Also contacting the eBay seller for help or instructions proved pointless as they said no ifurther instructions are available.