So I recently picked up a 98 a4 quattro 2.8 auto. Great car, except a few minor issues. One of the first things on my repair list is to fix the temp sensors. My temp gauge does nothing at all, doesnt move, jump around or anything like that. My buddy and co-worker told me that the car is equipped with two ect's on for the computer one for the gauge. I found the one behind the right cylinder head but were is the other? Also when i ordered the part they sent me a green sensor but the one that came out of the car is blue. Any difference? Thank you

There's no difference other than the color, I wondered the same when I got mine so I called the parts department and got my answer, youre good.

thought the green sensor was an updated version?

It is.The second sensor is screwed into the side of the radiator. It's almost always fine - the problematic one is the one on the crossover pipe behind the head, which you found.

Idk why I worded it that way lol